Cook sausage in a skillet until browned and crumbly. Remove to paper towels to drain. Add butter to skillet and melt. Add flour and stir into butter to form a roux, adding olive oil if necessary to incorporate all the flour. Add milk and cook, stirring until gravy is thickened and smooth.
Transfer gravy to a buttered or sprayed casserole dish. Cut biscuits into 1/8s and submerge them down into the gravy. Dish can be covered and refrigerated at this point, and can be left overnight for baking in the morning.
Uncover and bake at 350 for 30-40 minutes or until biscuits are cooked through and golden
Notes
If gravy is lumpy, use an immersion blender to smooth it out