Introduction

There’s just something magical about waking up on a weekend or a special holiday morning, knowing breakfast is practically ready before you even brew your first cup of coffee. No rushing around, no fuss! This Overnight Croissant Breakfast Casserole is one of those recipes that feels like a warm hug and a high-five all rolled into one. It’s incredibly simple to put together the night before, letting all those yummy flavors meld and the croissants soak up the custardy goodness. When morning arrives, you just pop it in the oven, and soon your home is filled with the most inviting aroma. It’s the perfect dish for lazy mornings, brunches with loved ones, or whenever you want to treat yourself without all the work!

Why You’ll Love This Recipe

Fast (prep is quick!)
Easy (seriously simple steps)
Giftable (makes a wonderful neighbor gift, unbaked with instructions!)
Crowd-pleasing (who doesn’t love croissants, sausage, and cheese?)

Ingredients

Here’s what you’ll need to gather for this morning masterpiece. Think simple, cozy goodness!

Large Croissants: About 6 of them. Day-old or slightly stale croissants work best here because they soak up the egg mixture beautifully without turning mushy.
Breakfast Sausage: 1 pound, cooked and crumbled. Use your favorite kind – mild, spicy, maple – whatever makes your heart happy!
Shredded Cheddar Cheese: 2 cups. Sharp cheddar is my go-to for that perfect tangy bite, but feel free to mix it up with Monterey Jack or a cheddar blend.
Large Eggs: 6 of them. These are the base of our creamy custard.
Milk: 2 cups. Whole milk gives the richest custard, but 2% or even a non-dairy milk like almond or soy milk can work too.
Salt: 1/2 teaspoon. Just enough to enhance the flavors.
Black Pepper: 1/4 teaspoon. Freshly ground is always best if you have it!
Dry Mustard: 1 teaspoon. This might sound a little unusual, but trust me! It adds a subtle depth and warmth that really elevates the savory flavors without tasting overtly like mustard.

How to Make It

Alright, let’s get this delightful casserole ready for its beauty sleep in the fridge!

Step 1: Prep Your Dish and Croissants. First, grab a 9×13 inch baking dish. Give it a good spray with non-stick cooking spray or grease it with butter. This makes serving and cleanup so much easier. Now, take those lovely croissants and tear or cut them into bite-sized pieces. Don’t worry about making them perfect – rustic is great! Scatter the pieces evenly across the bottom of your prepared dish. Think of them as little buttery pillows waiting to soak up flavor.

Step 2: Layer the Goodies. Once your croissants are settled, sprinkle the cooked and crumbled breakfast sausage right over them. Make sure it’s spread out so you get sausage in every bite. Next, pile on that wonderful shredded cheddar cheese, distributing it evenly over the sausage and croissants. It’s already looking good, right?

Step 3: Whisk the Custard. In a separate, medium-sized bowl, crack those 6 eggs. Add the milk, salt, black pepper, and that secret ingredient, dry mustard. Grab a whisk and give it all a good whisking until everything is well combined and the mixture looks smooth and slightly frothy. You want the yolks and whites completely blended.

Step 4: Pour and Soak. Carefully pour the egg and milk mixture evenly over the croissants, sausage, and cheese in the baking dish. Gently press down on the croissants with a spatula or the back of a spoon if needed, just to make sure they’re soaking up that delicious custard. You want every piece to get coated!

Step 5: The Overnight Rest (or Quick Nap). Cover the baking dish tightly. Plastic wrap works perfectly. Now, pop it in the refrigerator. The magic happens during this resting period. It needs at least 4 hours for the croissants to soak properly and the flavors to meld, but honestly, letting it chill overnight is the best way to go. It makes your morning so much simpler!

Step 6: Morning Bake Time! When you’re ready to bake, preheat your oven to 350°F (175°C). Take the casserole dish out of the fridge. It might be cold, so handle with care.

Step 7: Initial Bake. Place the covered dish in the preheated oven and bake for 30 minutes. Baking it covered helps ensure the center gets cooked through without the top browning too quickly.

Step 8: Uncover and Finish. After 30 minutes, carefully remove the cover. Return the dish to the oven and bake for another 15-20 minutes. You’ll know it’s done when the top is golden brown, the cheese is bubbly, and the center is set (not jiggly). You can test this gently with a spatula or knife in the middle.

Step 9: Rest Before Serving. Let the casserole stand for 5-10 minutes before you slice and serve. This allows it to set up a bit more, making it easier to cut and ensuring it’s not too hot to handle.

Substitutions & Additions

One of the best things about casseroles is how adaptable they are! Here are some ideas to make this recipe your own:

Different Meats: Swap the breakfast sausage for cooked and crumbled bacon, diced ham, or even cooked ground turkey sausage.
Veggies: Sauté some chopped onions, bell peppers, spinach, or mushrooms and add them along with the sausage and cheese layer.
Cheeses: Instead of just cheddar, try adding some Gruyère, Swiss, Monterey Jack, or a spicy Pepper Jack for a kick!
Herbs & Spices: Sprinkle in some dried or fresh chives, parsley, a pinch of paprika, or a dash of red pepper flakes to the egg mixture or over the top.
Bread: While croissants are divine, you could try this with other bread like brioche, challah, or even cubes of French bread, though the texture will be different. Make sure to use slightly stale bread if not using croissants.

Tips for Success

Use Stale Croissants: As mentioned, slightly stale croissants (a day or two old) are ideal. Fresh, super-soft ones can sometimes turn a little too mushy. If yours are very fresh, you can even lightly toast the cut pieces in the oven for a few minutes before assembling.
Don’t Skimp on the Soaking Time: The overnight rest is crucial for the best texture and flavor integration. If you’re really pressed for time, the 4 hours minimum is okay, but overnight is truly preferred.
Cook Sausage Thoroughly: Make sure your sausage is fully cooked and drained of excess grease before adding it to the casserole.
Check for Doneness: The casserole should be set in the center. If the top is browning too fast but the middle is still wobbly, tent it loosely with foil for the last few minutes of baking.
Prep Ahead: The beauty is the overnight assembly! You can cook the sausage and shred the cheese even a day or two before assembling the casserole.

How to Store It

If you happen to have any leftovers (a rare occurrence in my house!), let the casserole cool completely after baking. Then, cover the baking dish tightly with plastic wrap or foil, or transfer individual portions to airtight containers. Store in the refrigerator for up to 3-4 days. To reheat, you can warm individual slices in the microwave or cover the dish loosely with foil and warm in a 300°F oven until heated through.

FAQs

Here are a few common questions you might have:

Q: Can I prepare this assembly earlier than the night before?
A: I wouldn’t recommend assembling it more than 24 hours in advance. The croissants can break down too much if soaking for an extended period.

Q: Can I freeze this casserole?
A: While you can freeze baked breakfast casseroles, the texture of the croissants can sometimes change upon thawing and reheating, becoming a bit softer than when fresh. If you do freeze, bake it fully, let it cool completely, then wrap tightly before freezing for up to 1-2 months. Thaw overnight in the fridge before reheating.

Q: What’s the best way to know the center is cooked?
A: Gently insert a knife or fork into the center. If it comes out clean and the egg doesn’t look wet or runny, it should be done. The edges will be visibly set and likely pulling away slightly from the dish.

Q: Can I use smaller croissants?
A: Yes, you can, but you’ll need more of them to get the same volume of bread. Just make sure the dish is well-filled with croissant pieces.

Overnight Croissant Breakfast Casserole

An incredibly simple breakfast casserole made with croissants, sausage, and cheese soaked in a savory egg custard, prepared the night before and baked in the morning.

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Cook Time 45

Equipment

Baking dish 9x13 inch
Non-stick cooking spray or butter
Medium-sized bowl
Whisk
Spatula or spoon
Plastic wrap
Oven

Ingredients

6 Large Croissants Day-old or slightly stale work best
1 pound Breakfast Sausage cooked and crumbled
2 cups Shredded Cheddar Cheese Sharp cheddar, Monterey Jack or a blend
6 Large Eggs
2 cups Milk Whole milk recommended, can substitute 2%, almond, or soy
0.5 teaspoon Salt
0.25 teaspoon Black Pepper Freshly ground is best
1 teaspoon Dry Mustard

Instructions

Prep Your Dish and Croissants. First, grab a 9x13 inch baking dish. Give it a good spray with non-stick cooking spray or grease it with butter. Now, take those lovely croissants and tear or cut them into bite-sized pieces. Scatter the pieces evenly across the bottom of your prepared dish.
Layer the Goodies. Once your croissants are settled, sprinkle the cooked and crumbled breakfast sausage right over them. Make sure it's spread out so you get sausage in every bite. Next, pile on that wonderful shredded cheddar cheese, distributing it evenly over the sausage and croissants.
Whisk the Custard. In a separate, medium-sized bowl, crack those 6 eggs. Add the milk, salt, black pepper, and that secret ingredient, dry mustard. Grab a whisk and give it all a good whisking until everything is well combined and the mixture looks smooth and slightly frothy. You want the yolks and whites completely blended.
Pour and Soak. Carefully pour the egg and milk mixture evenly over the croissants, sausage, and cheese in the baking dish. Gently press down on the croissants with a spatula or the back of a spoon if needed, just to make sure they're soaking up that delicious custard.
The Overnight Rest (or Quick Nap). Cover the baking dish tightly. Plastic wrap works perfectly. Now, pop it in the refrigerator. It needs at least 4 hours for the croissants to soak properly and the flavors to meld, but letting it chill overnight is the best way to go.
Morning Bake Time! When you're ready to bake, preheat your oven to 350°F (175°C). Take the casserole dish out of the fridge.
Initial Bake. Place the covered dish in the preheated oven and bake for 30 minutes.
Uncover and Finish. After 30 minutes, carefully remove the cover. Return the dish to the oven and bake for another 15-20 minutes. You'll know it's done when the top is golden brown, the cheese is bubbly, and the center is set (not jiggly). You can test this gently with a spatula or knife in the middle.
Rest Before Serving. Let the casserole stand for 5-10 minutes before you slice and serve.

Notes

Use stale croissants (a day or two old) for best results; lightly toast fresh ones if needed. Don't skimp on the soaking time - overnight is preferred for best texture and flavor. Ensure sausage is fully cooked and drained before adding. If the top browns too fast while the center is still wobbly, tent loosely with foil. Casserole can be assembled up to 24 hours in advance. Store leftovers covered in the refrigerator for up to 3-4 days; reheat in microwave or 300°F oven. Freezing after baking is possible, but texture may change upon thawing.