Print

Savory Caramelized Onion & Gruyere Breakfast Casserole: Best Make-Ahead

Savory Caramelized Onion and Gruyere Breakfast Casserole - featured image
Print Recipe

A rich, savory breakfast casserole featuring deeply caramelized onions, nutty gruyere cheese, and a silky egg custard. Perfect for make-ahead brunch, holidays, or lazy weekend mornings.

Ingredients

Scale
  • 3–4 medium large yellow onions, thinly sliced
  • 3 tablespoons unsalted butter
  • 8 ounces gruyere cheese, grated
  • 8–10 large eggs, room temperature preferred
  • 1 ½ cups whole milk
  • ½ cup heavy cream
  • 6 cups day-old crusty bread (such as French baguette or sourdough), cubed
  • 1 tablespoon fresh thyme, chopped (or 1 teaspoon dried)
  • 1 teaspoon kosher salt
  • ½ teaspoon freshly ground black pepper
  • 1 teaspoon Dijon mustard

Instructions

  1. Caramelize the onions: Heat 3 tablespoons unsalted butter in a large skillet over medium heat. Add sliced onions and a pinch of salt. Cook, stirring every 5 minutes, for 30-40 minutes until deeply golden brown and soft. If onions stick, add a tablespoon of water and scrape up brown bits. Let cool slightly.
  2. Prepare the bread: Cut day-old bread into 1-inch cubes (about 6 cups). If bread is fresh, spread cubes on a baking sheet and toast at 300°F for 10 minutes. Let cool completely.
  3. Make the egg custard: In a large mixing bowl, whisk together 8-10 eggs, 1 ½ cups whole milk, ½ cup heavy cream, 1 teaspoon Dijon mustard, 1 tablespoon fresh thyme, 1 teaspoon kosher salt, and ½ teaspoon black pepper until smooth and uniform.
  4. Assemble the casserole: Spread half of the bread cubes evenly in a greased 9×13-inch baking dish. Sprinkle half of the caramelized onions over the bread, then half of the grated gruyere. Repeat with remaining bread, onions, and cheese. Pour egg mixture evenly over the dish, pressing down gently with a spatula to saturate the bread.
  5. Rest or refrigerate: Let casserole sit at room temperature for 30 minutes, or cover and refrigerate for up to 24 hours for make-ahead.
  6. Bake: Preheat oven to 350°F. If refrigerated, let sit on counter while oven preheats. Bake uncovered for 45-55 minutes until top is golden brown, edges are puffed, and a knife inserted in center comes out clean. If top browns too quickly, tent with foil for last 15 minutes.
  7. Rest before serving: Let casserole rest for at least 10 minutes before slicing to allow custard to set.

Notes

For best results, use day-old bread and grate gruyere from a block. Let casserole rest 10 minutes before serving. If making ahead, refrigerate assembled casserole up to 24 hours. Add 5-10 minutes to baking time if starting from cold. For a crispier top, reheat in toaster oven or air fryer.

Nutrition

Keywords: breakfast casserole, caramelized onion, gruyere, make-ahead brunch, egg casserole, holiday breakfast, savory casserole

Find it online: https://flurpchef.com/savory-caramelized-onion-and-gruyere-breakfast-casserole-best-make-ahead/