Heat a large cast-iron skillet over medium-high heat. Add the sausage, break it up with a wooden spoon, and cook, stirring occasionally, until well browned and cooked through, about 7 minutes.
Using a slotted spoon, transfer the sausage to a bowl, leaving the rendered fat in the skillet. Whisk the flour into the fat and cook, stirring, for about 1 minute. While whisking, pour the milk into the skillet and bring the gravy to a boil. Lower the heat and simmer gently for 2 minutes. Stir in the sausage and season with pepper. Split the biscuits in half and divide them among plates. Top each biscuit with some of the gravy and serve immediately