Croissant Breakfast Casserole

Active Time: 40 MinsTotal Time1 Hour 40 MinsChilling Time8 Hours
Yield: Serves 8

Our Test Kitchen has made dozens and dozens of breakfast casseroles over the years, but this one is our latest favorite. Made with day-old mini croissants, caramelized onions, and a rich and cheesy egg custard flavored with a touch of Dijon, this Croissant Breakfast Casserole is a real crowd-pleaser and can 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 get dark quickly, so be sure to tent it with foil while it finishes cooking.


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

How to Make It

Step 1

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; 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.

Step 2

Whisk together eggs, milk, mustard, salt, and pepper. 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 1/2 cup cheese. Cover with aluminum foil, and chill 8 hours or up to overnight.

Step 3

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.

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