Easy Overnight Croissant Breakfast Casserole

Overnight Croissant Breakfast Casserole is buttery, savory, and totally effortless when you need to feed a crowd! It has flaky croissants, Italian sausage, melty cheese, and a rich custard that soaks in overnight for the dreamiest breakfast bake.

Love More Breakfast Casseroles? Try My Crack Breakfast Casserole or this Farmer’s Casserole next.

Why You’ll Love This Recipe

Flaky, buttery, and wonderfully rich, this Overnight Croissant Breakfast Casserole makes mornings effortless and delicious. Layers of tender croissants, eggs, cheese, and savory breakfast meats soak overnight, then bake into a golden, custardy dish. Perfect for holidays or brunch gatherings, it’s an elegant yet easy make-ahead meal everyone will love.

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Ingredient List

Bread and Dairy:

• 4–6 large croissants (day-old preferred), torn into large pieces
• 12 large eggs
• 1 1/2 cups half-and-half
• 1 teaspoon dry mustard
• 1 teaspoon salt
• 1 teaspoon ground black pepper

Meat and Vegetables:

• 1 pound Italian or spicy sausage (ground or links removed from casings)
• 2 cups onions, chopped
• 1 tablespoon olive oil or butter (as needed for sautéing)
• 1–2 cups fresh spinach

Cheese:

• 2 cups grated cheese (cheddar, Monterey Jack, pepper jack, mozzarella, or a combo)

Optional Serving:

• Chili sauce or salsa

Why These Ingredients Work

Day-old croissants are the secret weapon here. They’re sturdy enough to soak up all that custard overnight without turning to mush, but still bake up buttery and tender with crispy golden edges. Fresh croissants are too soft and will fall apart.

Half-and-half gives you that rich, creamy custard without being too heavy. It’s the perfect balance between whole milk (too thin) and heavy cream (too rich).

Dry mustard might seem random, but trust me—it adds a subtle tang and depth that makes the whole dish taste more complex and “restaurant-quality.”

Italian sausage brings savory, slightly spicy flavor that cuts through the richness of the eggs and cheese. Make sure to drain it really well or your casserole will be greasy.

Fresh spinach wilts down to almost nothing but adds little pockets of color and a touch of earthiness. Plus, it makes this feel like a grown-up dish!

A cheese blend melts better and tastes more interesting than using just one kind. I always do at least two types for maximum gooey deliciousness.

Essential Tools and Equipment

• 9×13-inch casserole dish – The Pyrex one from our wedding registry that somehow survived 4 moves
• Large skillet – My black Calphalon nonstick pan I got at HomeGoods for $19.99
• Blender or large bowl – Ninja blender from Black Friday 2020 because I’m lazy
• Aluminum foil – Reynolds Wrap from the pantry
• Paper towels – Whatever’s on the Bounty holder on my counter

How To Make Overnight Croissant Breakfast Casserole

Step 1: Prep Your Casserole Dish

Spray Pam all over your 9×13 pan. Rip up the croissants with your hands into big chunks – don’t waste time with a knife, just tear them. Throw them in the pan. Some gaps are totally fine, mine always has gaps.

Step 2: Brown the Sausage

Squeeze the sausage out of the tube into your skillet on medium-high. Break it up with my wooden spoon from IKEA. Takes 7-8 minutes till it’s brown all over. Scoop it onto a plate piled with paper towels. Grab more paper towels and press down hard on the sausage to squish out all the grease. Like really smash it. Amy didn’t do this step right and I already told you what happened to her casserole. Spread the drained sausage over your croissant layer.

Step 3: Cook the Vegetables

Pour most of the grease out of your pan into an old Folgers can under the sink. If your pan looks too dry add a little butter. Dump in the onions and cook them till they look see-through and soft, maybe 5 minutes while you scroll TikTok. Throw in all the spinach and stir it around till it wilts and gets small. Like a minute. Spread this stuff over the sausage.

Step 4: Add the Cheese

Rip open both cheese bags and pour them all over the top. Shake the pan a little or use your hands to spread it so it’s not all in one blob.

Step 5: Make the Custard

Crack all 12 eggs into the blender. Pour in the half-and-half from the carton. Blend it till it looks smooth and yellow. Dump in the mustard, salt, and pepper. Blend again for like 5 seconds. If you’re doing this by hand with a whisk just beat it till you can’t see any stringy egg white parts floating around.

Step 6: Assemble and Refrigerate

Pour all the egg mixture slowly over the pan. Grab a fork and push down any croissant pieces floating on top because they need to get wet. Spray one side of your foil with Pam and cover the pan with the sprayed side down. Stick it in the fridge behind the milk and OJ. I make this around 9:30 or 10pm after Lily goes to bed and bake it at 8am the next morning.

Step 7: Bring to Room Temperature

Pull it out when you get up. Leave it sitting on the counter for 30-45 minutes while you make coffee and scroll your phone and get dressed. Last Mother’s Day I forgot this step and put cold casserole straight in the hot oven and the edges were burnt but the middle was still cold and raw. Jake’s mom was coming over in 20 minutes and I wanted to cry.

Step 8: Bake Covered

Turn the oven to 375. Put the covered pan in. Set a timer on your phone for 30 minutes.

Step 9: Bake Uncovered

Pull it out and take off the foil. Be careful there’s so much hot steam under there. Put the pan back in for another 30 minutes. The top should be puffy and golden. If it starts looking too dark before time’s up put the foil back on loose.

Step 10: Rest and Serve

This part is actual torture because it smells so good but you HAVE to wait 30 minutes.

You Must Know

Day-old stale croissants are required, this is not optional. I already told you about my $23 French bakery disaster. Don’t make my mistake. Buy them the day before and leave them on the counter overnight.

Drain the sausage till your arms hurt from pressing paper towels on it. So much grease comes out. Nobody wants to eat greasy casserole with orange oil pooling on top.

Let it sit out before baking. Cold to hot equals disaster. Trust me I’ve done it wrong enough times.

Pro Tips & Cooking Hacks

• You know it’s done when you shake the pan and the middle barely moves. Little tiny jiggle is okay, it keeps cooking while it sits.
• Spray the foil or all your cheese rips off stuck to it. Happened to me twice before I learned.
• I cook sausage on Sunday afternoons sometimes during meal prep and stick it in a Rubbermaid container till Thursday or Friday. Makes assembly take like 10 minutes total.
• Full 30 minutes of resting or forget it. You’ll have slop. No patience works against you here.
• Blender is so much faster than whisking. My arm gets tired after like 30 seconds of whisking.

Flavor Variations & Suggestions

Mexican version: Use pepper jack and Mexican blend cheese, dump in a can of Hatch green chiles from Trader Joe’s, serve with Pace salsa and Daisy sour cream.

Vegetarian version: My friend Sarah from yoga doesn’t eat meat and she loads it with mushrooms, bell peppers and zucchini instead. Says it’s great but I’ve never tried it because I like sausage.

All bacon: Cook a whole pound of Wright brand bacon till it’s crispy, crumble it all up, use that instead of sausage. Add chopped green onions from a bag. Jake’s friend Mike made this for fantasy football draft day.

Extra spicy: Two tubes of hot Italian sausage or dump in red pepper flakes. Jake does this version when his college roommates come visit and I can’t eat it.

Fancy version: Amy uses Gruyere and Swiss from the expensive cheese section at Whole Foods when she’s trying to impress her boss. Cost her like $18 in cheese alone.

With herbs: Linda adds fresh thyme with the onions. I never have fresh herbs so I skip it.

Make-Ahead Options

That’s literally why this recipe exists. Make it after dinner, bake it for breakfast.

Cook the sausage up to 3 days ahead if you want. I cooked it on Tuesday night in September and didn’t assemble the casserole till Friday morning for Saturday brunch.

Cooked sausage freezes perfect. Got a Ziploc bag in my freezer right now from October 3rd. Just move it to the fridge the night before to thaw.

Don’t make the whole thing more than one night ahead though. Mom made it on Thursday for Saturday Easter brunch in 2022 and said the texture was mushy and gross.

Don’t freeze the raw assembled casserole. Rachel tried it in June and said the eggs got grainy and weird when she baked it. You can freeze leftovers after it’s baked though, that works fine.

Recipe Notes & Baker’s Tips

• Costco croissants are massive so 4 is plenty. The regular ones from Kroger or Publix you need 5 or 6 to cover the pan bottom.
• No blender just means whisking by hand. Your arm will hurt but it works.
• My cousin Beth who lives in Boulder Colorado says she has to add 10 extra minutes to the covered baking time because of altitude.
• It puffs up like crazy while baking then goes back down when it cools. First time I made it in 2021 I thought I ruined it but Linda said that’s totally normal.
• Use Jimmy Dean mild sausage if little kids are eating. My nephew Lucas is 6 and he won’t touch anything spicy.

Serving Suggestions

It’s rich and heavy so you don’t need much else. I usually cut up whatever melon is on sale at Publix because I feel weird only putting one thing on the table.

Hot sauce or salsa on top makes it less heavy. Cuts through all the butter and cheese.

When my bunco ladies came over last month I set up a whole topping station – Pace salsa, Daisy sour cream, Cholula, a bag of cilantro from Walmart, and those Wholly Guacamole single cups from Costco. Everyone made their own plate and loved it.

Always make coffee. Sometimes mimosas if it’s after noon and nobody has to drive home right away.

How to Store Your Overnight Croissant Breakfast Casserole

Refrigerator: Let it cool for an hour then cover it with foil or plastic wrap. Lasts 3-4 days easy. My kids microwave leftovers for breakfast before school all week.

Freezer: Cut into 12 squares, wrap each piece tight in plastic wrap, throw them in a gallon Ziploc bag. Label it with a Sharpie. Good for 2 months. Thaw in the fridge overnight before reheating.

Reheating: Cover with foil, stick in a 325 degree oven for 15-20 minutes if it was in the fridge. Frozen pieces need like 25-30 minutes. Microwave is way faster but makes it rubbery and weird.

Room temperature: Don’t leave it sitting out more than 2 hours. Eggs go bad and you’ll get food poisoning. Ask me how I know (just kidding I don’t know, I’ve just heard horror stories).

Allergy Information

Contains: Eggs, dairy, wheat, pork

Gluten-free: Whole Foods has gluten-free croissants in the freezer section for like $8.99. Check your sausage package label because some brands put wheat in as filler. Johnsonville doesn’t.

Dairy-free: This is basically impossible to do. You could try Violife shredded cheese and Oatly oat milk instead of half-and-half but I’ve never tested it so I have zero clue if it works. Probably tastes completely different.

No eggs: Can’t do this recipe without eggs. They’re literally the entire base. No substitute exists.

No pork: Trader Joe’s turkey sausage is decent. They also have chicken sausage.

Questions I Get Asked A Lot

My casserole turned out watery—what happened?

You definitely didn’t drain the sausage enough. Or you cooked the spinach too long and all the water came out. You need to drain that meat like crazy, use half a roll of Bounty. And cook the spinach for literally one minute just till it’s limp. Also you MUST let it sit for the full 30 minutes after baking or it won’t set up firm.

Do I have to use half-and-half, or can I use milk?

I ran out of half-and-half once in July and used whole milk. It was thinner and less creamy but Jake ate it fine. Add a couple tablespoons of melted butter to make it taste richer if you’re using regular milk.

How do I know when it’s fully cooked in the center?

Grab the pan with oven mitts and shake it back and forth. The middle should barely wiggle, not slosh around like water. I stick a butter knife in the center and if it comes out mostly clean with just a tiny bit of egg on it, it’s done. If there’s liquid raw egg on the knife it needs more time.

💬 Tried this recipe? Leave a comment and rating below! Did you go spicy with the sausage? What did you serve on the side?