3 tbsp. unsalted butter
3 tbsp. olive oil
5 large yellow onions, halved & thinly sliced
2 tsp. salt
1 cup water
12 cups chicken or beef broth
1 tbsp. chicken or beef base
4-5 sprigs of fresh thyme, tied together with kitchen twine (or substitute with 1 tsp. dried thyme)
3 fresh bay leaves (or 2 dried leaves)
1/2 cup dry white wine or dry sherry
1/2 tsp. black pepper
French bread or baguette
Swiss or Gruyere cheese
1. Melt butter with olive oil in a large stock pot over medium high heat. Add sliced onions, season with 1 tsp. salt & stir well. Cover and let onions sweat for about 10 minutes until translucent.
2. Remove cover, and continue cooking until most of liquid has evaporated, stirring occasionally.
3. Reduce heat to medium low and cook for about 1 hour, stirring frequently and scraping up any brown bits that form on the bottom of the pan (you can deglaze the onions with a small amount of water a couple times during the long cooking period). Cook until onions are very soft, very reduced and have turned a deep brown color.
4. Add the chicken or beef broth, chicken or beef base, water, white wine, black pepper, thyme and bay leaf. Bring up to a simmer and cook for about 30 minutes. Discard the thyme & bay leaf. Turn off heat and season with salt and 1/2 tsp. black pepper.
5. Serve piping hot. If you like French bread and cheese on top, just heat up your broiler, adjust the shelves to about 6" from the top, ladle soup into broiler-proof bowls, top with a slice of bread sprinkled with grated cheese or cheese slices. Broil until cheese is brown & soup is bubbly, about 5-10 minutes. Cool 5 minutes before serving.
If you don't want to go through the hassle of broiling, just place a slice of cheese on the bottom of each serving bowl, ladle the soup over, then top with a slice of toasted baguette. As with many soups & stews, this will taste better the next day.