Heat the oven to 375°F, or use the temperature specified on the refrigerated biscuit dough package. Lightly grease a 13 x 9-inch baking dish with nonstick cooking spray or a little butter.

Separate the biscuits and cut each into several small pieces, generally quarters or eighths. Arrange about half of the pieces across the bottom of the prepared baking dish.

Brown the sausage in a large skillet over medium heat, breaking it into small crumbles as it cooks. Drain excess grease if necessary, leaving enough moisture in the skillet to help flavor the gravy.

Sprinkle the flour over the cooked sausage and stir for about 1 minute. This cooks the raw flour taste and helps create a smoother gravy.

Gradually whisk in the whole milk, then add the salt and black pepper. Cook, stirring frequently, until the gravy reaches a gentle boil and thickens, usually in 4–7 minutes.

Stir the sausage into the gravy, then pour the mixture over the biscuit pieces in the baking dish. Arrange the remaining biscuit pieces evenly over the top.

Bake on the center oven rack for about 25–30 minutes, until the biscuits are puffed and golden and the gravy is bubbling. Let the casserole stand for 5 minutes before serving.