1 teaspoon salt
5 large sweet onions, thinly sliced
3 (14 ounce) can beef broth
1/2 cup red wine
1 tablespoon Worcestershire sauce
1 sprig fresh thyme leaves
1 bay leaf
1 tablespoon balsamic vinegar
Salt and freshly ground black pepper to taste
French or Italian bread, cut in thick slices and toasted
8 slices Gruyere and Havarti cheese slices, room temperature
Melt the butter in a large pot over medium heat. Add the onions and salt. Cook 35 minutes, stirring frequently, until onions are caramelized.
Add the broth, red wine, Worcestershire sauce, thyme and bay leaf. Simmer over medium heat for 20 minutes, stirring occasionally. Remove and discard the herbs. Reduce the heat to low, mix in the balsamic vinegar and season with salt and pepper.
Preheat oven broiler. Toast one thickly sliced piece of bread for each bowl of soup you are serving.
Arrange oven- safe bowls on a rimmed baking sheet. Fill each bowl 2/3 full with hot soup. Top each bowl with 1 slice toasted bread, sliced Gruyere cheese and Havarti cheese.
Broil 5 minutes, or until bubbly and golden brown. As it softens, the cheese will cascade over the sides of the crock and form a beautifully melted crusty seal.
Serve immediately on cool, crisp nights! Makes 6 servings.