Preheat oven to 400 degrees. Spray a 2 1/2-quart casserole dish (approx. 7x10-inch) with cooking spray.
Open biscuits, and cut biscuits into quarters. Layer half of the quarters in prepared pan. Bake for 10 minutes.
Meanwhile, prepare gravy. In a large skillet, brown and crumble the sausage over medium-high heat until cooked through and no longer pink. Using a wood spoon, stir flour into sausage until completely absorbed. Lower the heat to medium. Add warm milk, stirring to combine. Season with salt and pepper. Stir frequently until mixture comes to a slight boil and thickens.
Pour the sausage gravy over the cooked biscuits. Layer the remaining uncooked, quartered biscuits over the gravy.
Place the casserole dish on a baking sheet and bake for 20-25 minutes. Lightly cover the casserole with foil the last 10 minutes of cooking to prevent biscuits from burning. Serve immediately.