In same skillet, melt butter over medium heat. Stir in flour (mixture will be thick). Slowly add 2 cups milk to skillet, beating constantly with whisk. Once all of the milk has been incorporated, increase heat to medium-high. Cook about 5 minutes or until thickened, beating constantly with whisk. Stir in the cooked sausage, 1 teaspoon salt and 1/2 teaspoon pepper; remove from heat.