Melt butter, cook onions and mushrooms until tender (about 5 minutes), then remove from pan and save. Brown meat in this pan in batches to remove excess moisture.
Save ⅔ cup of broth. Mix remaining broth in meat with ketchup and garlic. Stir and simmer for 15 minutes. Mix ⅔ cup broth with ⅓ cup flour and stir into meat mixture. Add saved onion and mushrooms mixture, then heat to boiling for 1 minute. Stir in sour cream. Serve over egg noodles.