Put the sausage in a pan over medium heat and break up with a spoon. Cook about 10-15 minutes, until browned and cooked through.
Remove sausage with a slotted spoon and put on a plate to save for later.
Turn pan to low-medium and add butter and flour. Whisk butter and flour until the butter is melted about 1 minute.
Slowly pour in the milk as your whisking, this deglazes the pan and prevents lumps.
After all the milk is added simmer the gravy for a few minutes until it thickens slightly. Then return the sausage to the pan and season with salt and pepper to taste. If the gravy is too thick, stir in milk about 1 tablespoon at a time.