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A serving of croissant breakfast casserole with eggs, sausage, and melted cheese sits on a floral-patterned plate. In the background, there’s a croissant and a red baking dish, perfect for trying new breakfast casserole recipes.
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French Onion Croissant Casserole

Buttery croissants soak up a rich thyme-infused egg mixture, layered with sweet caramelized onions and melted Gruyère. This casserole rests overnight, then bakes into a golden, savory masterpiece perfect for breakfast or brunch.
Prep Time50 minutes
Cook Time50 minutes
Resting Time15 minutes
Total Time1 hour 55 minutes
Course: Breakfast, lunch
Cuisine: American
Keyword: breakfast casserole recipes, croissant breakfast casserole, croissant egg bake, french onion croissant casserole
Servings: 8 servings

Equipment

  • 1 frying pan
  • 1 9x13 baking dish

Ingredients

Onions

  • 2 tbsp vegetable oil
  • 2-3 yellow onions sliced
  • 1 tbsp balsamic vinegar

Casserole

  • 6 croissants cubed
  • 5 eggs
  • 1 cup heavy cream 33%
  • 1/2 cup 2% milk
  • 1½ cups gruyere cheese shredded
  • 1 tbsp dijon mustard
  • 1 tsp garlic powder
  • 1/2 tsp onion powder
  • 1 tsp dried parsley
  • 1 tsp dried thyme
  • 1/2 tsp black pepper
  • pinch salt
  • fresh thyme to garnish
  • balsamic glaze to garnish

Instructions

  • Caramelize the onions: slice the onions into thin slices or finely chop them, depending on your preference.
    Bring a medium-sized saucepan to low-medium heat.
    Add the vegetable oil, and once warm, add the onions.
    Toss the onions with a wooden spoon so that all of the oil evenly coats them.
    Slowly cook the onions on a gentle simmer for 45 to 60 minutes. This will develop a deep caramelization and rich flavor.
    Optional: if you notice the pan is absorbing too much liquid, deglaze with about a tablespoon of water as needed, to prevent the onions from sticking.
    Once the onions are deeply golden, jammy, and caramelized, deglaze with the balsamic vinegar, stir to combine then remove the onions from the heat and set aside until ready to use.
  • While the onions are cooling, prepare your casserole. Grab a 9x13 baking dish and spray it with a neutral cooking oil.
  • Tear your croissants into cubes and layer them evenly in the prepared baking dish.
    Spoon the caramelized onions into the crevices between the croissant cubes, ensuring they are evenly distributed throughout the dish, then layer on the shredded gruyere cheese.
    Set aside while you prepare your egg mixture.
  • In a medium-sized bowl, add the eggs, heavy cream, milk, dijon mustard, garlic powder, onion powder, dried parsley, dried thyme, black pepper, and a pinch of salt. Whisk thoroughly until everything is well combined.
  • Pour the egg mixture evenly over the croissant pieces, making sure it is distributed across the entire dish.
  • Using the back of a wooden spoon or a spatula, gently press the croissant mixture down so that the croissants are almost submerged in the egg mixture.
  • Cover the casserole with aluminum foil and refrigerate it ideally overnight, or for at least 1 hour.
  • When ready, preheat your oven to 350°F. Ideally, remove the casserole from the fridge about 30 minutes before baking to let it take the chill off.
  • Bake the casserole covered for about 30 minutes. Then uncover it and bake for an additional 25 to 30 minutes, or until it’s fully set. Keep an eye on it, as baking times may vary by oven.
  • Finish with a drizzle of balsamic glaze.
  • Let it cool on the counter for at least 10 minutes before slicing and serving.

Nutrition

Calories: 447kcal | Carbohydrates: 25g | Protein: 14g | Fat: 32g | Saturated Fat: 17g | Polyunsaturated Fat: 4g | Monounsaturated Fat: 8g | Trans Fat: 0.04g | Cholesterol: 185mg | Sodium: 278mg | Potassium: 206mg | Fiber: 2g | Sugar: 8g | Vitamin A: 1095IU | Vitamin C: 2mg | Calcium: 261mg | Iron: 2mg
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