This is the best Homemade French Onion Soup! It has a generous portion of caramelized onions in a rich, flavorful beef broth made from scratch. The cheese is broiled on top of croutons to melty, toasty perfection.
Caramelize your onions in a Dutch oven or thick-bottomed skillet.
Once your onions are sufficiently caramelized (deep, rich caramel in color) sprinkle with the flour and stir to coat. Add the thyme, Cognac, two large pinches of kosher salt, and a few grinds of pepper. Stir to distribute the spices and allow to cook on low for a few minutes.
Add your beef broth and simmer over low heat for 30-40 minutes. This allows the flavors to develop.
While your soup is simmering, toast your bread on a baking sheet under the broiler. Watch it carefully! Toast until brown on each side.
Ladle an equal amount of soup into each broiler-safe, 13-ounce bowl. Top with several bread slices and then top with ¼ of the cheese mixture. Broil on a baking sheet until the cheese has melted and has started to bubble and brown.
Serve immediately, but eat with care! It will be very hot.
Notes
Technique - Be patient and let your onions caramelize completely. They should be a caramel brown, fragrant, sweet, and soft when ready.Storage - You can store leftover soup in an airtight container in the fridge for 3 to 4 days. If you plan to have leftovers, I recommend cooling the soup and storing it before adding the baguette and cheese.Based on this fantastic French Onion Soup Recipe by Martha Stewart.