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Great for Christmas morning, or weekend brunch with family, this Overnight Sausage Croissant Breakfast Casserole with Leeks is an easy, flavorful breakfast you can prep the night before and pop in the oven with no work the morning of!

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If you’re looking for a simple, flavorful, wake-and-bake breakfast for Christmas morning, or just any morning you want to live deliciously- this casserole is for you. Made with croissants, crumbled breakfast sausage, leeks, gruyere and a creamy egg mixture- this custardy casserole is easy, cheesy, and crowd-pleasy.

Overnight Sausage Croissant Breakfast Casserole with Leeks

Prep it and forget it

To make this sausage casserole, which walks the line between strata and quiche, you will need:

  • A touch of butter.
  • Some breakfast sausage. Either the ground stuff, or the links, removed from their casings.
  • 1 leek, tough green ends removed, halved lengthwise, cleaned and sliced thinly. 
  • A bunch of eggs.
  • Some heavy cream.
  • Salt and fresh ground black pepper, to taste- always.
  • Garlic powder.
  • 6 store-bought medium-large Croissants, torn into small pieces.
  • 6 oz Gruyere cheese, shredded by hand.
breakfast casserole ingredients

To make the casserole, you’ll cook up the sausage and leeks, and layer them over torn croissants in a greased baking dish.

torn croissants, breakfast sausage and leeks

Next, whip up the eggs and cream with a bit of seasoning, and pour that over the sausage, leeks, and croissants. Cover the mixture generously with fresh shredded gruyere, then cover the whole thing with foil, and pop it in the fridge!

pouring on the egg and cream mixture

Baking the casserole

When you’re ready to eat, preheat your oven to 375 degrees, and take the casserole out of the fridge while the oven preheats. Bake it covered for 30 minutes, then uncovered for another 25-30 minutes, until its brown, bubbly and set. Allow the casserole to cool, and serve! This casserole doesn’t need a thing, but feel free to serve it with a touch of hot sauce, if that’s your thing.

This casserole is great for an easy and delicious family breakfast, or as a brunch dish for a potluck!

adding the shredded gruyere

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If you make my Overnight Sausage Croissant Breakfast Casserole with Leeks, please be sure to leave me a comment! I would love to hear from you, and value your feedback! Lastly, if you make the recipe and love it, please tag me on Instagram! I love to see your photos!

More Breakfast Recipes:

Ragin’ Cajun Frittata

Prosciutto Pesto Frittata
Crab Imperial Eggs Benedict

Green Eggs and Ham Breakfast Pockets

Overnight Sausage Croissant Breakfast Casserole with Leeks
Overnight Sausage Croissant Breakfast Casserole with Leeks
Print Recipe
5 from 1 vote

Overnight Sausage Breakfast Casserole

Prep Time10 mins
Cook Time1 hr 13 mins
Total Time1 hr 23 mins
Course: Breakfast, Brunch
Keyword: breakfast, casserole, sausage
Servings: 8


  • 1 tbsp butter
  • 12 oz breakfast sausage (removed from casing, or ground)
  • 1 leek- tough ends removed, cleaned halved lengthwise and sliced thinly  
  • 10 large eggs
  • 1 1/4 cups heavy cream 
  • salt and fresh ground black pepper, to taste
  • 1 tsp garlic powder 
  • 6 medium-large Croissants, torn into small pieces 
  • 6 oz gruyere cheese, shredded 


  • Prepping the casserole
    1. In a large non-stick skillet, melt butter over medium heat.
    2. Add the sausage to the pan and cook, breaking up as you go, until brown, 5-6 minutes.
    3. Add the leeks to the pan with the sausage, season with salt and pepper, and cook, stirring occasionally, for 5-7 minutes- until leeks are softened.
    4. While sausage and leeks cook, tear up the croissants into small pieces, and layer in the bottom of greased 9”x13” glass or ceramic baking dish.
    5. Once sausage and leeks are ready, layer evenly over croissant pieces.
    6. In a large mixing bowl, whisk eggs and cream together, and season with salt, pepper and garlic powder.
    7. Pour egg mixture evenly over croissants, sausage and leeks.
    8. Top casserole with grated gruyere cheese, and cover the dish with foil.
    9. Refrigerate overnight. Can be made up to a day in advance.
    Bake the casserole
    1. Preheat the oven to 375 degrees.
    2. Bake the casserole covered for 30 minutes. After 30 minutes, uncover the dish and bake for an additional 25-30 minutes, until casserole is set, and top is brown and crispy. Allow to cool about 20 minutes before serving.

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