In a large skillet, cook beef and onion over medium heat until meat is no longer pink; drain. Add bacon and garlic.
Combine the flour, salt, paprika and nutmeg; gradually stir into beef mixture until blended.
Stir in soup and mushrooms(mixture will be thick). Bring to a boil. Reduce heat; simmer, uncovered, for 4-5 minutes or until heated through. Stir in sour cream. Cook 3-4 minutes longer or until heated through; stirring occasionally(do not boil). Serve on buns.