Step 1: Brown the Sausage
In a large skillet over medium-high heat, cook the breakfast sausage, breaking it up with a wooden spoon until it is thoroughly browned and crumbled. Use a slotted spoon to transfer the cooked sausage to a paper towel-lined plate to drain any excess grease. This step is crucial to prevent a greasy casserole.

Step 2: Prepare the Creamy Egg Mixture
In a very large mixing bowl, whisk the 6 eggs until they are light and uniform. Add the whole milk, sour cream, and the can of cream of mushroom soup. Whisk vigorously until the mixture is as smooth as possible. Don’t worry if there are tiny lumps from the soup; they will dissolve during baking. Whisk in the garlic powder, onion powder, black pepper, and salt.

Step 3: Assemble the Casserole Layers
Grease a 9×13 inch baking dish thoroughly with butter or non-stick spray. Spread the 8 cups of cubed bread evenly in the bottom of the dish. Sprinkle the cooked, drained sausage evenly over the bread layer. Now, sprinkle 1 ½ cups of the shredded cheddar cheese over the sausage.

Step 4: The Custard Soak
Slowly and carefully pour the egg and sour cream mixture evenly over the entire casserole. Use a spatula or your hands to gently press down on the bread, ensuring every cube soaks up some of the creamy custard. This is the key to a uniform, non-dry texture.

Step 5: The First Chill
Sprinkle the remaining ½ cup of cheddar cheese over the top. Cover the baking dish tightly with plastic wrap and refrigerate for a minimum of 4 hours, but ideally overnight (8-12 hours). This resting period is mandatory for the bread to fully absorb the custard.

Step 6: Create the Iconic Topping
Just before baking, preheat your oven to 350°F (175°C). In a medium bowl, combine the crushed Ritz crackers, melted butter, grated Parmesan cheese, and poppy seeds. Stir until the cracker crumbs are evenly coated in the butter and the mixture resembles wet sand.

Step 7: Bake to Golden-Brown Perfection
Remove the casserole from the refrigerator and take off the plastic wrap. Sprinkle the buttery cracker topping evenly over the entire surface. Place the dish in the preheated oven and bake for 45-55 minutes, or until the top is deep golden brown and crispy, the edges are bubbling, and the center is fully set (no longer jiggly).

Step 8: Rest and Serve
Remove the casserole from the oven and let it rest for 10-15 minutes before serving. This allows the internal structure to set, making it easier to cut into clean squares. Serve hot and watch it disappear