This is a red onion version that is really nice:
Red onion soup - French recipe
3 tablespoons vegetable oil
2 tablespoons unsalted butter
3 cloves garlic, thinly sliced
2 pounds red onions, thinly sliced
1/4 cup dry white wine
1/4 cup balsamic vinegar
1/4 cup flour
4 cups beef broth
4 cups chicken broth
1/2 teaspoon dried thyme
1 bay leaf
Long French baguette bread
2 large cloves peeled garlic
Salt and ground black pepper
1/4 cup cream, optional
2 cups grated French Gruyere cheese
Recipe
1. In a 12-inch casserole or saucepan, heat the oil and butter. When the oil and butter are hot, add the garlic and onions, and stir fry for a minute.
2. Cover and simmer over low heat for 15 minutes, stirring to make sure the onions dont burn.
3. Add the wine and vinegar and cook for a minute to evaporate some of the alcohol. Add the flour and stir for a minute.
4. Add the beef and chicken broth, thyme and bay leaf, and over medium heat, bring to a boil.
5. Whisk, cover and simmer, over low heat for 30 minutes.
6. Preheat the oven to 350 degrees F.
7. Cut the French bread diagonally into 2 centimetre thick slices, and toast them in the oven
8. Rub each side of the toast slices with garlic.
9. Season the soup with salt and pepper. Stir in the cream if used and remove the soup from the heat.
10. Scatter some grated cheese on one side of the toasted bread and broil until cheese is golden.
11. Garnish each portion with two cheese-covered bread rounds.