Place hamburger in a large, deep skillet. Crumble and cook over medium high heat until evenly brown. Remove from heat and sprinkle flour over cooked hamburger. Stir until evenly coated and all fat is absorbed.
Place skillet over medium heat, add 1/2 of milk and stir until gravy begins to thicken. Add remaining milk until desired consistency has been reached and gravy comes to a boil. Season with salt, pepper and onion salt.
Serve over mashed or boiled potatoes, toast or biscuits. Add fresh chopped onion if desired.
