How to make a delicious French Onion Soup Recipe. The ingredients are 5 large onions, 1 stick of butter, 1 tsp of salt and 1 tbsp of flour. Melt butter in a large pot, add sliced onions, salt and cook the onions on low medium heat for about an hour to caramelize. Stir the onions repeatedly so it doesn’t burn. Once caramelized mix in flour and cook for another few minutes before adding 16 - 24 ounces of beef stock. You can buy beef broth to save time or you can make it. I cooked 2 pounds of beef bones in water with celery, leeks, carrots, onions, pepper corns and salt. Covered with a lid and simmered for 2 hours before draining and add stock to my caramelized onions. Bring pot to a boil and add a few sprigs of thyme and a dash of Worcestershire. Next pour soup in an oven safe bowl, top with bread and Gruyère cheese. Lastly Broil for 5 minutes in the oven.