How To Caramelize Onions In Half The Time, Plus A French Onion Soup Recipe

Get out some baking soda and your Instant Pot.
Use this trick to quickly caramelize onions for French onion soup.
Use this trick to quickly caramelize onions for French onion soup.

What’s better than a hot bowl of French onion soup on a chilly winter day? It’s amazing that with just a few simple ingredients you can have an incredibly flavorful bowlful. But the problem is, it takes so much time ― first you have to caramelize the onions, and then you have to assemble the soup and let it simmer to develop those complex flavors. Luckily, with the help of an Instant Pot and a fun chef trick to speed up the caramelization process, this recipe cuts the cooking time in half.

Years ago, while working in professional kitchens, I learned about the magical powers of baking soda. Did you know that adding just a little bit of it to your onions will make them caramelize faster? The baking soda increases the pH level of the onions, speeding up the Maillard reaction, which causes them to brown faster. I love making this soup in an Instant Pot because the pressure not only makes it all cook faster, but it helps develop strong, in-depth flavors.

This French onion soup isn’t like all the other French onion soups out there. First, I like to add sliced fennel with the onions while they caramelize. The sharp, slightly bitter fennel adds some contrast to the sweetness of the onions. I deglaze the pan with red wine to add richness and acidity. I use nice hunks of sourdough bread as the garnish, because the tanginess of sourdough is the perfect vessel to hold globs of creamy, gooey Gruyere cheese. I garnish with grated Parmesan cheese to add a salty note, and freshly ground black pepper.

This soup can be made ahead of time and stored in the fridge for four or five days. You can even freeze the base of the soup, making for a super quick dinner option when you want a rich soup but don’t have hours to wait for it to cook. Just top the base with a slice of a toasted baguette and cheese, and dinner is ready in minutes.

French Onion Soup

Serves 4 to 6

Ingredients:

  • 4 tablespoons unsalted butter

  • 5 large yellow onions, peeled and cut into 1/2-inch slices

  • 2 fennel bulbs, cut into 1/2-inch slices

  • 1/4 teaspoon baking soda

  • 4 cloves garlic, minced

  • 2 teaspoons fresh thyme leaves

  • 1/2 cup dry red wine

  • 1 bay leaf

  • 6 cups beef stock

  • 1 tablespoon Worcestershire sauce

  • Sourdough baguette, cut into 1-inch-thick slices

  • 1 cup shredded Gruyere cheese

  • 1/4 cup grated Parmesan cheese

  • Kosher salt and freshly ground black pepper

Directions

1. Turn on the Instant Pot and select sauté mode on high.

2. Melt butter, then add onions and fennel. Cook for 5 to 7 minutes until softened, then add baking soda and continue to cook, stirring occasionally, until golden brown and caramelized, about 20 to 25 minutes.

3. Add garlic and thyme and cook until fragrant, about 1 to 2 minutes.

4. Add red wine. Use spatula to scrape up any browned bits on bottom of pot. Let wine reduce by half, about 2 to 3 minutes.

5. Add bay leaf, beef stock, Worcestershire and 2 teaspoons kosher salt.

6. Seal pressure cooker lid and cook on high pressure for 20 minutes. Use the quick release method to remove pressure.

7. Preheat oven to broiler setting.

8. Evenly ladle soup into oven-safe bowls. Top each bowl with 1 to 2 baguette slices, a few tablespoons of Gruyere cheese and 2 to 3 teaspoons Parmesan cheese.

9. Place under broiler and cook until browned and cheese is melted, about 2 minutes.

10. Garnish with freshly ground black pepper and enjoy.

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