French onion soup is usually made with beef stock. I’ve made delicious soup with stock from the leftover rib and chine bones of a rib roast.
French onion soup (Soupe à l’oignon) is an onion and beef broth or a beef stock based soup traditionally served with croutons and cheese as toppings.
The rich flavor of the base is not due just to the broth, but to the caramelized onions. Caramelization, in this case, is the procedure in which the onions are cooked slowly until the melting sugars approach burning temperature, becoming brown.
1 1/2 pounds (about 5 cups) thinly sliced yellow onions
1 tablespoon olive oil
3 tablespoons all-purpose flour
8 cups beef or other brown stock
1 teaspoon dried thyme
2 cloves garlic, minced
4 slices French bread
4 slices provolone cheese
1/4 cup grated Parmesan cheese
Melt butter with olive oil in a pot on medium heat. Add the onions, toss to coat them in oil and cover the pot. Reduce the heat to low and let them slowly cook for 15 minutes. Cover the lid.
After 15 minutes, uncover the pot, raise the heat slightly and stir in the salt.
Cook onions, stirring frequently, for 30 to 40 minutes until they have turned an even, deep golden brown.
After the onions are fully caramelized, sprinkle with flour and cook, stirring, for 3 minutes.
Add minced garlic and thyme. Season with salt and pepper, and simmer for 30 minutes.
Add stock in it. Bring to a simmer and simmer partially covered for 30 to 40 more minutes, skimming if needed.
Ladle the soup into the bowls or casserole dish. Layer each slice of bread with a slice of provolone, 1/2 slice Diced Swiss and 1 tablespoon Parmesan cheese. Place bowls on cookie sheet and boil in the preheated oven until cheese bubbles and browns slightly. Serve immediately.