Croissant Breakfast Casserole Recipe

Active Time:

40 mins

Chill Time:

8 hrs

Total Time:

9 hrs 40 mins

Servings:

8

Our Test Kitchen has made dozens and dozens of breakfast casseroles over the years, but this croissant breakfast casserole is a favorite still. Made with day-old mini croissants, caramelized onions, and a rich and cheesy egg custard that is flavored with a touch of Dijon, this croissant breakfast casserole is a real crowd-pleaser.

It can also be made ahead. Assemble the casserole and store it, unbaked, in the refrigerator overnight. Then, in the morning, all you have to do is pop it in the oven. Keep an eye on the casserole as it bakes. The buttery croissants exposed on top can get dark quickly, so tent it with foil, if needed, while it finishes cooking.

Ingredients for Croissant Breakfast Casserole

To make this casserole, you'll need:

Ham steaks: Chopped and browned for a meaty bite. Substitute with crumbled bacon or browned sausage, if preferred.
Olive oil: For cooking the ham, onions, and spinach.
Vidalia or other sweet onions: Caramelized for a rich, sweet flavor in the casserole.
Baby spinach: Wilted into the mix for color and freshness.
Large eggs: Helps bind and set the casserole.
Whole milk: The liquid base of the casserole filling. Other types of milk can be used if needed, or a combination of 2 percent milk and half-and-half.
Dijon mustard: Adds a tangy flavor that contrasts the ham, onions, and cheese.
Kosher salt and black pepper: Enhances the flavor.
Fontina cheese: A nutty, buttery flavor. Can be substituted with other shredded cheeses, including Cheddar, gruyere, gouda, or provolone.
Day-old mini croissants: Can substitute with regular croissants (if large, cut into chunks), whether day-old or fresh, as well as cubed brioche, challah, or other types of enriched breads.

How To Make Croissant Breakfast Casserole

Full instructions are below, but here's a brief recap before you get started:

Step 1. Coarsely chop ham and cook with 1 tablespoon of oil until fat is rendered. Transfer to a bowl, reserving drippings in skillet. Add onions and cook until deeply browned, about 30 minutes. Add spinach; cook until wilted. Add mixture to bowl with ham; cool 10 minutes.
Step 2. Whisk together eggs, milk, mustard, salt, and pepper. Stir into ham along with 1 cup of cheese. Arrange croissants in a lightly greased 11- x 7-inch baking dish; cover with egg mixture and remaining cheese. Cover with foil, and chill 8 hours or up to overnight.
Step 3. Preheat oven to 375°F. Uncover casserole and place on a baking sheet. Bake until golden brown, about 1 hour. Shield with foil after 25 minutes, if needed, to prevent excess browning.

What To Serve with Croissant Breakfast Casserole

This meaty, cheesy casserole is a perfect dish to place on the table for a large family-style breakfast or brunch. Serve with a side of fresh fruit salad, side salad, heirloom tomatoes, crispy hash browns, or something sweet like warm cinnamon rolls for a hearty meal everyone will remember.

How To Store and Reheat Leftover Croissant Breakfast Casserole

Refrigerate leftover croissant casserole for up to three days, or freeze for up to three months. Thaw overnight in the refrigerator if frozen, and reheat in a preheated 350ºF oven until hot throughout before serving.

More Make-Ahead Breakfast Casserole Recipes You'll Love

There's nothing better than going to bed knowing that an impressive breakfast is just waiting to be baked first thing in the morning. When you're serving a crowd, these recipes have you covered:

Editorial contributions by Katie Rosenhouse.

Ingredients

2 (5-oz.) country ham steaks, trimmed, bone discarded
2 Tbsp. olive oil, divided
1 1/2 lbs. Vidalia onions or other sweet onions (2 medium onions), chopped (4 cups)
3 oz. baby spinach, roughly chopped (3 cups)
6 large eggs
2 cups whole milk
2 tsp. Dijon mustard
1 tsp. kosher salt
1 tsp. black pepper
6 oz. fontina cheese, shredded (about 1 1⁄2 cups), divided
1 lb. (about 15) day-old mini croissants

Directions

Cook ham:

Coarsely chop ham. (You should have 1 1/2 cups.) Heat 1 tablespoon of the oil in a large skillet over medium. Add ham; cook, stirring occasionally, until fat is rendered, about 4 minutes. Using a slotted spoon, transfer ham to a large bowl, reserving drippings in skillet. Add remaining 1 tablespoon oil to skillet.
Cook onions and spinach:

Stir in onions. Cook, stirring occasionally, until deeply browned, about 30 minutes. Add spinach; cook, stirring often, until wilted, 1 to 2 minutes. Transfer onion mixture to bowl with ham; let cool 10 minutes.
Make egg mixture:

Whisk together eggs, milk, mustard, salt, and pepper.
Arrange croissants, and add egg mixture:

Add egg mixture and 1 cup of the cheese to bowl with onion mixture, and stir to combine. Arrange croissants, slightly overlapping, in 2 rows in a lightly greased 11- x 7-inch baking dish. Pour mixture over croissants. Sprinkle with remaining ½ cup cheese
Chill casserole:

Cover with aluminum foil, and chill 8 hours or up to overnight.
Bake casserole:

Preheat oven to 375°F. Uncover casserole, and place on a large rimmed baking sheet. Bake in preheated oven until golden brown and center is set, about 1 hour. Shield with foil after 25 minutes, if needed to prevent excess browning.

Frequently Asked Questions

What can I add to this casserole in the place of ham steaks?

Substitute the ham steaks with cooked crumbled bacon or sausage. You can also leave the ham out entirely, or substitute with a vegetarian option like mushrooms.
Do the croissants for this croissant casserole have to be day-old?

Day-old croissants tend to hold up better in a baked casserole, leaving you with a hearty result rather than a soggy one. If using fresh croissants, you can toast them lightly in the oven and cool before using for a similar result.
Why is my breakfast casserole soggy?

If you cover the casserole for a portion of the bake time, uncover for the final minutes to create a crisp, browned topping. Using day-old croissants will also help keep the casserole from becoming soggy.
How can I tell when my breakfast casserole is done?

The finished casserole should be golden brown on top, and firm to the touch in the center when pressed.