Preheat your oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish with butter or non-stick spray.

In a large skillet over medium-high heat, cook the ground sausage, breaking it apart with a spoon, until it's fully browned and crumbled. Do not drain the grease.

Reduce the heat to medium. Sprinkle the all-purpose flour over the cooked sausage and grease. Stir continuously for 1-2 minutes to cook out the raw flour taste, creating a roux.

Gradually pour in the 3 cups of whole milk while whisking constantly to prevent lumps. Continue to cook, stirring frequently, until the gravy comes to a simmer and thickens, about 5-7 minutes.

Once thickened, remove the skillet from the heat. Stir in the 1/2 tsp black pepper, 1/4 tsp salt, and the pinch of cayenne pepper (if using). Set aside.

Open the can of biscuits and cut each biscuit into quarters.

Arrange the biscuit pieces in a single, even layer across the bottom of the prepared baking dish.

In a large mixing bowl, whisk together the 8 large eggs, 1/2 cup of milk, 1/2 tsp salt, and 1/4 tsp black pepper until well combined and slightly frothy.

Pour the prepared sausage gravy evenly over the biscuit pieces in the baking dish.

Slowly and evenly pour the egg mixture over the sausage gravy.

Sprinkle the 2 cups of shredded cheddar cheese evenly over the top of the casserole.

Bake uncovered for 35 to 40 minutes, or until the eggs are set in the center and the top is golden brown and bubbly. You can check for doneness by inserting a knife into the center; it should come out clean.

Let the casserole rest for 10 minutes before slicing and serving. This allows it to set up and makes for cleaner slices.