Slice the onions thinly. In a Dutch oven, add butter and melt over medium heat.
Add onions and sugar. Cook stirring occasionally, until they soften and caramelize, about 20–25 minutes.
Sprinkle in the flour and stir for 30 seconds to coat the onions.
Pour in the red wine, stirring to deglaze the pot.
Slowly add the beef broth and water, mixing as you go.
Add thyme, rosemary, pepper, and garlic powder. Stir to combine.
Bring the soup to a gentle simmer and cook for 10 minutes. Remove herb stems before serving.
To serve: Ladle the hot soup into bowls. Sprinkle cheese on top, let it melt for a minute, and serve with crusty bread on the side.
