Cook the sausage in a large, heavy skillet over medium-low heat, stirring to break it into small chunks. Cook until no longer pink and almost as brown as you like. This will take about 10 minutes. Discard all but about 3 tbsp. drippings. Add the onion to the sausage and drippings, and cook until the onion is softSprinkle the flour over the sausage and onions, tossing gently with a fork or wooden spoon until they’re coated. Continue to cook and stir until the flour is golden-brown. This should take only a few minutesCook and stir for a few minutes until the gravy has thickened, scraping the bottom as you cook to incorporate any browned bits on the bottom of the pan. Split the baked biscuits and place on individual plates. Ladle the sausage gravy over them and serve.