In a large skillet over medium high heat, cook the sausage until brown and crumbly. If excess oil, drain while keeping a solid tablespoon of the sausage oil in the pan. Add the butter and stir well until melted.
Sprinkle sausage with flour, stir, and allow to cook for several minutes.
Add the milk and stir. Continue stirring occasionally over medium heat until gravy thickens, 5-10 minutes.