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Croissant Breakfast Casserole
4.3 from 57 votes

Croissant Breakfast Casserole

Croissant Breakfast Casserole layers sautéed mushrooms, leeks, and onions with smoked ham, gruyere, and Parmesan cheeses inside torn croissants soaked in an egg and milk custard. The casserole is chilled overnight then baked until golden and set, yielding a rich, savory dish with crisped edges and a tender center, ideal for a make-ahead breakfast or brunch.

Prep Time
20 mins
Cook Time
1 hr
Additional Time
8 hrs
Total Time
9 hrs 20 mins
Servings: 8 -10 servings
Course: Breakfast

Ingredients

  • ¼ cup butter plus extra for buttering the pan, unsalted, Challenge brand
  • 8 ounces mushrooms such as crimini or shiitake, fresh, sliced
  • 1 large leek sliced
  • 1 medium onion diced
  • 1 teaspoon salt divided, fine sea salt
  • 3-4 cloves garlic minced
  • 2 tablespoons whole-grain mustard
  • 1 tablespoon sherry vinegar optional
  • 8 large egg
  • 2 cups milk whole
  • 6-8 ounces smoked ham diced
  • 6 ounces gruyere cheese grated
  • 2 ounces Parmesan Cheese freshly grated
  • ½ teaspoon black pepper
  • 12 ounces croissants cut or torn into 1-inch pieces

Instructions

    Cup of Yum
  1. In medium pan, melt the butter over medium heat. Add the mushrooms, leeks, and onion with ¼ teaspoon of the salt. Saute for about 10 minutes. When the mushrooms and onions are soft and caramelized, add the garlic, mustard, and sherry vinegar and cook for 1 additional minute. Set aside to cool.
  2. In a large bowl, whisk the eggs and milk until thoroughly combined. Add the cooled mushroom mixture, ham, cheeses, and black pepper, and remaining ¾ teaspoon of salt. Gently fold in the croissant pieces. 
  3. Generously butter a 9x13-inch baking dish. Add the casserole mixture to the pan. Cover and refrigerate overnight. 
  4. In the morning, preheat the oven to 375ºF. Bake the casserole for 1 hour, or until the top is golden, the edges are crispy, and the center is set.