Description

This Overnight Croissant Breakfast Casserole is the ultimate make-ahead brunch recipe featuring flaky croissants soaked in a savory custard with Italian sausage, cheese, spinach, and onions. Assemble it the night before and bake fresh in the morning for an effortless crowd-pleasing breakfast that tastes like you worked all morning!

Ingredients

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

Cook Mode Prevent your screen from going dark

Instructions

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.

Notes

Test for doneness properly: The casserole is done when the center is set but still has a slight jiggle (it will continue cooking as it rests). If you overbake it, the eggs can get rubbery.
Spray that foil! Seriously, spray the underside of your foil before covering. Cheese sticks like crazy and you don’t want to lose all that golden goodness on the foil.
Make the sausage ahead: Cook and drain your sausage up to 3 days in advance and store it in the fridge. You can even freeze cooked, drained sausage for up to a month. This makes assembly super quick!
Don’t skip the resting time: I know I already said this, but it’s SO important. That 30-minute rest after baking is what transforms this from a runny mess into perfect, sliceable squares.
Use a blender for the custard: It takes 30 seconds and gets you the smoothest, creamiest custard with zero lumps. If you whisk by hand, you have to work harder to get rid of those egg streaks.

Prep Time: 25 minutes
Cook Time: 1 hour + Inactive Time: 8 hours (overnight refrigeration) + 30 minutes resting
Category: Breakfast
Method: Baking
Cuisine: American