Begin by melting 12 ounces of butter in a 6-quart soup pot over low heat. This sets the stage for caramelizing the onions. As the butter melts, it creates a rich base that will enhance the flavor of the soup.
Add 4 cups of sliced onions to the pot. Stir them gently, ensuring they are coated in the melted butter. Keep the heat low to allow the onions to soften without browning, stirring occasionally for about 20 to 25 minutes until they turn a beautiful golden color.
Once the onions are caramelized, add 1 3/4 cups of all-purpose flour. This will help thicken the soup and give it a hearty texture. Stir continuously for about 5 to 10 minutes to cook out the raw flour taste.
Gradually add in 12 cups of beef stock, stirring constantly to avoid lumps. The stock is what gives the soup its rich depth of flavor, so make sure to use a quality product. Bring the mixture to a gentle boil.
Add 1/2 teaspoon of cayenne pepper and 1 1/2 tablespoons of salt. This seasoning will elevate the flavor profile of your soup. Adjust to taste, but remember that the cheese on top will add more saltiness.
Reduce the heat and let the soup simmer for about 15 minutes. This allows the flavors to meld beautifully. During this time, take a moment to enjoy the wonderful aroma wafting through your kitchen.
Remove the pot from the heat and prepare a small bowl. Beat 1 egg yolk and 2 tablespoons of cream together. Take a ladle of the hot soup and mix it with the egg mixture to temper it. Then slowly add this back into the soup pot while stirring. This technique adds a creamy texture to the soup.
Preheat your oven to 350°F. On a baking sheet, arrange 8 slices of toasted French bread and sprinkle each slice with ½ cup of grated Parmesan cheese. This will create a delicious, cheesy topping that is essential for your French Onion Soup.
Ladle the soup into small bowls, placing a slice of the cheesy French bread on top of each bowl. This will soak up the flavors from the soup and create a delightful texture contrast.
Finally, place the bowls under the broiler for a few minutes until the cheese melts and begins to turn golden brown. Remove them from the oven and serve immediately while it’s hot and bubbly!
