In a skillet, cook the sausage over medium heat, breaking it into crumbles until browned (7-10 minutes).
Sprinkle flour over the sausage, stir, and cook for 2 minutes.
Gradually pour in milk while stirring to avoid lumps. Simmer until thickened (5 minutes).
Season with salt, pepper, sage, and red pepper flakes. Adjust to taste.