Cook sausage in a large skillet over medium-high heat until browned and crumbly, 5 to 7 minutes. Transfer sausage to a plate, leaving drippings in the skillet.
Sprinkle flour over sausage and reduce the heat to medium. Stir sausage until flour is integrated.
Gradually whisk in milk until smooth. Bring to a simmer and season with salt and pepper. Cook, stirring occasionally, until mixture is smooth and thick, 10 to 15 minutes.
