Step 1: Preparing the Sausage Mixture

Begin by heating the olive oil in a large skillet over medium heat. Once the oil is hot, add the chopped onion and sauté it for about 5-7 minutes, until it becomes soft and translucent. The onions will release their natural sweetness, infusing your kitchen with a comforting aroma that sets the stage for the rest of the dish.

Next, crumble the breakfast sausage into the skillet with the onions. Cook the sausage until it’s browned and fully cooked, breaking it apart with a wooden spoon as it cooks. This process should take around 7-10 minutes, and you’ll want to ensure the sausage is cooked through, with no pink remaining. Once the sausage is browned, remove the skillet from the heat and drain any excess fat from the sausage mixture, but make sure to save a small amount of the fat for the gravy. Set the sausage mixture aside and let it cool slightly while you prepare the croissants.

Step 2: Preparing the Croissants

Take your croissants and tear them into bite-sized pieces. The goal is to create small chunks of croissant that will soak up the egg mixture and provide a tender, custardy texture. If you don’t have large croissants, you can use smaller ones—just tear enough to cover the bottom of your 9×13-inch baking dish.

In a large mixing bowl, combine the torn croissants with the cooked sausage mixture and half of the shredded cheddar cheese. Gently toss everything together, ensuring that the croissant pieces are evenly coated with sausage and cheese. This will create a flavorful base that will bake up beautifully in the oven.

Step 3: Preparing the Egg Mixture

In another bowl, whisk together the eggs, heavy cream, ½ cup of whole milk, dry mustard powder, salt, black pepper, paprika, and garlic powder. The mustard powder and paprika add a subtle kick to the dish, enhancing the flavors without overpowering them. The egg mixture will be the binding element, holding the croissant pieces, sausage, and cheese together. Once everything is well combined, pour the egg mixture evenly over the croissant mixture in the baking dish. Use a spoon or spatula to press the mixture down slightly to ensure that all of the croissant pieces are submerged in the egg mixture.

Step 4: Refrigerating the Casserole Overnight

Cover the baking dish with a lid or plastic wrap and refrigerate it overnight. The waiting time allows the croissants to soak up the egg mixture and absorb all the flavors, resulting in a perfectly tender, custardy casserole when baked. The sausage and cheese also have time to meld together, making each bite a symphony of savory goodness. If you’re in a rush and don’t have time to refrigerate it overnight, let the casserole sit in the fridge for at least 2 hours before baking.

Step 5: Baking the Casserole

The next morning, preheat your oven to 350°F (175°C). Once the oven is heated, remove the casserole from the fridge and uncover it. Place the dish in the preheated oven and bake for 35 to 45 minutes. The casserole should turn golden brown on top, and the egg mixture should be fully set. If you prefer a crispier top, you can broil the casserole for an additional 2-3 minutes at the end of baking. As the casserole bakes, your kitchen will fill with the mouthwatering scent of melted cheese, sausage, and freshly baked croissants, making it even harder to wait for that first bite.

Step 6: Making the Gravy

While the casserole bakes, prepare the gravy. In a small saucepan, melt the butter over medium heat. Once the butter has melted, add the reserved sausage fat and stir until the mixture is smooth. Then, add the flour, stirring constantly for about 1 minute to form a roux. The roux will thicken the gravy and give it a rich, velvety texture.

Gradually add the remaining 2 ½ cups of milk, whisking as you go to prevent any lumps. Continue stirring until the gravy thickens to your desired consistency. This should take about 5 minutes. Once thickened, season with salt and pepper to taste. The gravy should be smooth, creamy, and flavorful, the perfect accompaniment to the casserole.

Step 7: Serving the Casserole

Once the casserole is out of the oven, let it cool for a few minutes before serving. This will give the casserole time to set and allow for easier slicing. Serve the casserole hot, spooning generous portions onto plates. Ladle the creamy sausage gravy over the top of each serving or serve the gravy on the side for dipping.