This recipe from Bon Appetit January 1998 is more akin to an oniony potato soup than the traditional French onion soup. If you want to make it truly vegetarian substitute the chicken broth with vegetable broth.
2 tablespoons butter
5 cups onion - sliced
2 large garlic clove - halved
5 cups chicken broth
8 ounces potato - cut into 1" cubes
1/2 cup whipping cream
1 tablespoon dry sherry
1 teaspoon fresh thyme - minced
chives - minced
Melt butter in heavy large pot over medium heat. Add onions and saute until very tender and pale golden, about 25 minutes. Add garlic and stir one minute. Add broth and potato and bring to boil. Reduce heat; cover and simmer until potato is very tender, about 25 minutes. Cool slightly.
Working in batches, puree soup in blender. Stir in cream, sherry, and thyme. Simmer about 10 minutes. Season with salt and pepper. Can be made 2 days ahead. Sprinkle with chives before serving.
Calories: 213 Calories From Fat: 57%
Protein: 4g Carbohydrate: 19g
Cholesterol: 39mg Sodium: 1356mg