4 T butter
1 tsp salt
2 large red onions, thinly sliced
2 large sweet onions, thinly sliced
1 (48 oz) container of chicken broth
1 (14 oz) can beef broth
1/2 c red wine
1 T Worcestershire sauce
2 springs fresh parsley
1 spring fresh thyme
1 bay leaf
1 T balsamic vinegar
salt and pepper to taste
4 slices French or Italian bread
8 slices Gruyere or Swiss cheese slices - room temperature
4 pinches paprika
Melt butter in a large pot over medium-high heat. Stir in salt, red onions and sweet onions. Cook 35 minutes, stirring frequently until onions are caramelized and almost syrupy.
Mix chicken broth, beef broth, wine, Worcestershire sauce into pot. Bundle parsley, thyme and bay leaf with twine and place in pot. Simmer over medium heat for 20 minutes, stirring occasionally.
Remove and discard herbs. Reduce heat to low. Mix in vinegar and season with salt and pepper. Cover and keep over low heat to stay hot while you prepare the bread.
Preheat broiler. Arrange bread slices on a baking sheet and broil 3 minutes, turning once until well toasted on both sides. Remove from heat; do not turn off broiler. Arrange 4 large oven safe bowls or crocks on a rimmed baking sheet. Fill each bowl 2/3 full with hot soup. Top each bowl with 1 slice of toasted bread, 2 slices of cheese. Sprinkle a little paprika on each bowl.
Broil 5 minutes or until bubbly and golden brown. As it softens, the cheese will cascade over the sides of the crock. Serve immediately