Break the sausage into large chunks and brown in a skillet (I like cast iron). 

Once the sausage is cooked through, add the butter and stir until it's melted. Slowly stir in the flour and continue to stir until it starts to turn golden.

Whisk in the butter milk and then the regular milk. Keep whisking until it's fully blended, then continue to stir with a wooden spoon. When the gravy is thickened, add salt and pepper to taste. 

Set on the back burner to keep warm or serve it up right now - smothering a big biscuit.