In this Prosciutto, Brie, & Swiss Croissant Breakfast Casserole, lightly toasted croissants, salty prosciutto, creamy brie, and sweet caramelized onions are mixed with a rich, eggy custard and topped with buttery Swiss cheese, creating a rich and decadent casserole. With the option to make ahead, it is sure to impress for any breakfast or brunch.

I have a good one for you today! Honestly, I have been so excited to share this recipe. I feel a little guilty for not sharing it sooner, because over the last few months, this has become one of our favorite brunch casseroles to share with friends. I made it when having friends over for my birthday and have taken it to multiple friends’ houses for brunch. It has basically become a staple at any brunch gathering.

So it seems fitting that I am finally sharing it here, just in time for Easter. Whip up this croissant breakfast casserole for your Easter brunch, and I promise all of your guests will be impressed!

This Caramelized Onion, Prosciutto, Brie, & Swiss Croissant Breakfast Casserole is easy to make (perfect for a busy holiday morning), but it is so rich, elegant, and delicious. The croissants mix with and absorb the custardy mixture, softening just slightly and becoming something entirely new. It is reminiscent of a bread pudding, but they stay light and airy, while getting crispy on the top and bottom. Plus, the added bites of gooey brie and salty prosciutto, along with sweet caramelized onions distributed throughout, make this breakfast casserole super decadent.

How Do You Make Caramelized Onion, Prosciutto, Brie, & Swiss Croissant Breakfast Casserole?

Making this Caramelized Onion, Prosciutto, Brie, & Swiss Croissant Breakfast Casserole is easy. Caramelizing the onions is a little time consuming, but with my easy short cut to caramelized onions, the process takes only about 30 minutes. Thus giving you time to prepare everything else while the onions cook.

For the onions, I use my new technique to quick caramelized onions inspired by this Swiss, Caramelized Onion, and Sausage Frittata. The trick is to cover them for the first half of cooking. I always used to caramelize onions in an open pan over very low heat, closely watching and stirring constantly to keep them from burning. This also meant I usually had to keep adding extra butter as well. However, by putting the onions in a pan with just a couple of tablespoons of butter, and covering them for the first 15 minutes of cooking, the liquid begins to cook out and the onions start to soften more quickly. Then finishing the onions uncovered for 5 – 10 more minutes allows them to caramelize up just perfectly.

The casserole can be made ahead of time, which makes it great for busy holidays or weekend brunches. Just be sure not to let the croissants sit in the egg custard mixture for more than an hour or two before baking, as they can become soggy. See the recipe notes for more on making this casserole bake ahead.

Other Variations of Croissant Breakfast Casserole

Another great thing about this Croissant Breakfast Casserole (as if you even needed another reason to love it!) is that it can be customized to your tastes. I have added thin sliced deli ham instead of prosciutto and you could swap out the Swiss for cheddar or Monterey jack cheese if you are not a fan. You can also add some sliced mushrooms in with the onions for about the last 10 minutes of cooking to caramelize them as well or just substitute mushrooms for the caramelized onions completely.

A friend even used premade pie crust instead of the croissants and she said it turned out great. She cut the crust into strips, rolled them up, and baked them before adding them to the custard mix. I will definitely have to try that some time.

My friend and I were also talking about how you could also make this into a sweet casserole instead of savory by keeping out the prosciutto, cheese, and onions and adding things like cinnamon, some berries, and vanilla. I will get to work on a sweet version soon and report back soon!

In the meantime, I hope you enjoy this Prosciutto, Brie, & Swiss Croissant Breakfast Casserole.

Looking for More Breakfast Recipes?

If you are looking for more recipes for breakfast or your Easter brunch, I have you covered whether you are serving a crowd or just two. Here are some of my favorites:

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Caramelized Onion, Prosciutto, Brie, & Swiss Croissant Breakfast Casserole

Prep Time25

Cook Time45

Total Time1 10

Course: Breakfast, Brunch

Cuisine: American

Keyword: brunch, caramelized onions, casserole, cheesy, croissants, eggs

Servings: 8

Ingredients

10 oz day-old croissants (about 12 mini croissants or 6 regular)
4 tablespoons unsalted butter (divided)
2 medium white onions (thinly sliced)
kosher salt and pepper
2 cloves garlic (minced or grated)
2 teaspoons dried thyme
1 cup heavy cream
1 cup milk
4 eggs (beaten)
2 tablespoons dijon mustard
1/2 teaspoon cayenne pepper (more or less to taste)
4 ounces prosciutto (torn)
4 ounces creamy Brie cheese (rind cut off & cubed)
1 cup Swiss cheese (shredded)
2 tablespoons everything bagel seasoning

Instructions

Preheat the oven to 350°
In a heavy skillet, melt 2 tablespoons butter over medium heat. Add the sliced onions and stir to coat the onions in the butter. Cover and cook 15 minutes, stirring after about 7 minutes to make sure they don’t burn. Uncover onions, and continue to cook 5 – 10 more minutes until the onions are soft and caramelized. Add the garlic and thyme, cook an additional minute. Remove from the heat and set aside.
While the onions cook, grease a 9 x 13-inch baking dish with cooking spray. Roughly tear croissants into medium size chunks. Arrange the torn croissants in the baking dish and lay 2 tablespoons of thinly sliced butter over the croissants. Transfer to the oven and bake 5-8 minutes, until the croissants are lightly toasted.
In a large bowl, whisk together the cream, milk, eggs, mustard, cayenne, and a pinch each of salt and pepper. Add the toasted croissants, onions, prosciutto, and Brie, gently stir to combine. Pour the mixture back into the casserole dish. Top with Swiss cheese and sprinkle with everything seasoning.
Cover with foil and bake for 30 minutes. Remove the foil, and continue baking for another 10-15 minutes or until the croissants are golden on top. Serve warm.

Notes

To Make a Few Hours Ahead: This can be prepped and assembled a few hours ahead of time and kept in the fridge. But keep in mind, you don’t want to let the croissants sit in the custard for more than 1 – 2 hours, as they will break down too much and become soggy.

To Make the Night Before: Complete the recipe through step 3. For step 4, keep the croissants separate (I just store mine in the Pyrex casserole dish with the lid on). Keep the custard mixture (without the croissants) in a sealed container in the fridge. When ready to assemble, remove from the fridge and toss the croissants with the egg mixture, then assemble in baking dish. Bake as directed.

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