Bake the biscuits according to the package directions.
While the biscuits bake, brown the breakfast sausage in a large, deep skillet over medium-high heat, breaking it apart as it cooks. Do not drain the grease.
Reduce the heat to medium-low. Add the butter and stir until melted.
Sprinkle the flour over the sausage and stir until evenly coated. Cook for about 1 minute.
Slowly pour in the milk, stirring continuously.
Simmer over low heat for 3–5 minutes, stirring frequently and scraping the bottom and sides of the skillet, until the gravy thickens.
Stir in the salt and pepper.
Split the warm biscuits and spoon the hot sausage gravy over the top. Serve immediately.
Notes
Refrigerate the leftovers in an airtight container for up to 1 week.