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Christmas Breakfast Casserole

A comforting, make-ahead breakfast casserole featuring savory pork sausage, caramelized onion, and toasted sourdough soaked in a creamy egg custard, topped with Gruyère and Parmesan cheese.
Print Recipe
Prep Time 30 minutes
Cook Time 1 hour
Total Time 1 hour 30 minutes
Servings: 8 servings
Course: Breakfast, Brunch
Cuisine: American
Calories: 450
Ingredients Method Notes

Ingredients
  

Main Ingredients
  • 1 lb pork breakfast sausage
  • 1 large yellow onion, chopped
  • 1 1-pound loaf sourdough bread, cut into 1-inch cubes
  • 2 cups shredded Gruyère cheese
  • 1/2 cup grated Parmesan cheese
Custard Ingredients
  • 8 large eggs
  • 2 cups whole milk
  • 1 cup heavy cream
  • 1 tbsp Dijon mustard
  • 1 tsp salt
  • 1/2 tsp black pepper
  • 1/4 tsp ground nutmeg

Method
 

Preparation
  1. Cook sausage and onion in a skillet until browned. Drain the grease.
  2. In a large bowl, combine bread cubes, sausage mixture, and cheeses. Transfer to a greased 9x13-inch baking dish.
  3. In the same bowl, whisk together all egg custard ingredients.
  4. Pour the custard evenly over the bread mixture. Cover and refrigerate for at least 8 hours or overnight.
Baking
  1. Preheat oven to 350°F (175°C). Let the casserole sit at room temperature for 30 minutes.
  2. Bake uncovered for 50-60 minutes until golden and set. Let rest for 10 minutes before serving.

Notes

Slice into squares and serve warm directly from the baking dish. Garnish with chopped chives or parsley for color. Refrigerate leftovers tightly covered for up to 4 days. For freezing, cut into portions and wrap tightly for up to 2 months.