Brown the ground beef sausage in a skillet over medium heat until fully cooked. Do not drain all the fat; leave about 2 tablespoons in the pan.
Sprinkle the flour over the cooked beef sausage and stir constantly for 2 minutes to cook out the raw flour taste.
Transfer the coated beef sausage mixture to the slow cooker.
Gradually whisk in the whole milk, heavy cream, salt, and black pepper until well combined.
Cover and cook on low for 2 to 3 hours, stirring occasionally, until the gravy reaches your desired thickness.
About 20 minutes before serving, bake the refrigerated buttermilk biscuits in the oven according to the package directions.
Split the warm biscuits in half and generously pour the hot beef gravy over the top before serving.