Preheat oven to 375°. Mix the first 5 ingredients. Add beef; mix lightly but thoroughly. Press about 1/3 cupful into each of 12 ungreased muffin cups.
Bake 15 minutes. Brush tops of loaves with 3 tablespoons ketchup; bake until a thermometer reads 160°, 5-7 minutes. If desired, serve with additional ketchup.
Freeze option: Bake muffins without ketchup; cover and freeze on a waxed paper-lined baking sheet until firm. Transfer muffins to an airtight freezer container; return to freezer. To use, partially thaw in refrigerator overnight. Place muffins on a greased shallow baking pan. Spread with ketchup. Bake in a preheated 350° oven until heated through.