Preheat the oven to 350 degrees and spray a 9x13 baking dish with nonstick cooking spray. Spread half the biscuit pieces in the bottom of the pan in an even layer and bake in the oven for 15 minutes, until the biscuits are golden brown.

While the biscuits are baking, brown the sausage in a large skillet. When the sausage is cooked, transfer it to a paper towel-lined plate.

Place the butter in the pan with the sausage drippings and stir until the butter is melted.

Add the flour and stir to mix. Cook until the mixture begins to bubble, stirring constantly.

When the flour mixture has thickened, add the milk and whisk to combine all the ingredients. Reduce heat to low and simmer until the gravy has thickened, stirring occasionally.

After the gravy has thickened, remove the pan from heat and stir in the sausage.

Pour the gravy mixture over the baked biscuits, making sure to cover them completely.

Layer the remaining biscuit pieces over the top of the casserole and return the pan to the oven. Bake for 15 to 20 minutes, until the biscuits on top are golden brown.