Step 1

In a large pot, saute sliced onions with the butter and olive oil.

Step 2

Add the sugar as this will help caramelize.

Step 3

Cook for 20-30 minutes until nicely browned. Add the thyme, basil, and season with salt and pepper, to taste. Cook for 1 minute.

Step 4

Add the beef broth and let simmer for 30 minutes. Add the sherry and the vinegar. Simmer for additional 5 minutes.

Step 5

Pour into individual bowls. Garnish with croutons and cheese. Serve immediately. If you would like melted cheese, broil the soup for a minute.