Melt the butter in a 6-quart pot or saucepan. Add the sliced onions and saute them until browned.
Add the beef broth, chicken broth, flour, sherry, water, black pepper, ketchup, salt, thyme, garlic powder, and optional hot sauce.
Reduce heat to low and simmer for 20 minutes. Serve with crusty bread.
Optional: Add asiago cheese as a topping before serving.
