Pre-heat oven to 350 degrees. In a large bowl, mix together 1/3 cup condensed French onion soup with ground beef, bread crumbs, egg, onion, garlic, salt and black pepper. Shape into 6 oval patties. In a large skillet over medium-high heat, brown both sides of patties. Pour off excess fat. In a small bowl, blend flour and remaining french onion soup along with cream of mushroom soup until smooth. Mix in ketchup, water, Worcestershire sauce and mustard powder. Pour over meat in skillet. Cover, and cook in oven for 30 minutes.