Heat a large skillet over medium-high heat. Add in ground sausage. Use a spatula to break up the sausage into small pieces and cook until sausage is browned and cooked through, about 8 minutes.
Stir in all purpose flour until no white powder remains.
Slowly add in milk, stirring constantly. Bring to a boil. Reduce heat to low and simmer until sauce is thickened, 2 to 3 minutes.
Season with salt and pepper to taste. Serve hot over toast or biscuits.