adapted by There's Always Thyme to Cook
Source: Sage Cuisine
2 tablespoons butter
3 tablespoons olive oil
6 cups onions, sliced
1 shallot chopped
1/2 teaspoon brown sugar
salt and pepper to taste
1 tablespoon balsamic vinegar
3 tablespoons Sherry
4 cups beef stock
4 cups chicken stock
1 bay leaf
4 slices of toasted French bread
Gruyere cheese or any good melting cheese you like
Heat butter and oil on medium heat; add onions, salt, sugar and shallot. The onions will very slowly caramelize, stir regularly, you are looking for the onions to become golden brown. This will take over thirty minutes or more. You don't want the onions to burn, so keep an eye.
Deglaze the pan with the sherry, and allow to reduce for 2-3 minutes.
While the onions are almost done caramelizing, add the chicken and beef broth in a stock pot; add the balsamic vinegar and bay leaf. Bring to a boil; reduce heat to medium. Add the onions and simmer for about 20-30 minutes. Remove bay leaf.
At this point you can store it the fridge or the freezer.
Preheat broiler for 5 minutes.
Toast bread in toaster or under broiler until golden brown; set aside.
Place 4 ovenproof soup bowls on baking sheet or pan. Ladle soup into bowls. Top with toast slices. Add cheese evenly over top.
Place tray of bowls under broiler; broil for about 3 minutes or until cheese is bubbly and golden. Be very careful, the bowls will be extremely hot.