Costco French Onion Soup Recipe (Made From Scratch)

Last Updated: August 15, 2026

The French Onion Soup most people mean when they search for a Costco version is actually a specific frozen product, the Cuisine Adventures brand, sold in the freezer section and heated up at home rather than made fresh in the store. It’s a good shortcut for a quick lunch, but it’s not the same as a proper from-scratch French onion soup with deeply caramelized onions and a rich broth.

This Costco French Onion Soup Recipe builds that from-scratch version, made with real caramelized onions and a broth with actual depth, instead of the frozen brick.

Why You’ll Love This Recipe

Most quick versions of French onion soup rush the onions, which is the one step you really can’t skip past. Slowly caramelizing them until they’re deeply golden is what gives the broth its flavor, and it’s worth the wait. This version also skips the wine most recipes call for, using a splash of vinegar instead to get the same brightness without any alcohol.

Ingredients

• 4 large yellow onions, thinly sliced
• 2 tablespoons butter
• 2 tablespoons olive oil
• 1 1/2 teaspoons salt, plus more to taste
• 2 cloves garlic, minced
• 1 tablespoon fresh thyme (or 1 teaspoon dried)
• 2 teaspoons all-purpose flour
• 6 cups beef broth
• 1 bay leaf
• 1/2 teaspoon black pepper, plus more to taste
• 1/4 teaspoon red wine vinegar or sherry vinegar
• 1 baguette, sliced into 3/8-inch rounds
• Olive oil, for brushing the bread
• 1 cup grated Gruyère cheese

Essential Kitchen Equipment

• Large heavy-bottomed pot or Dutch oven
• Wooden spatula
• Chef’s knife
• Cutting board
• Baking sheet
• Oven-safe soup bowls or ramekins
• Ladle

Step By Step Guide

Step 1: Heat the butter and olive oil in a large pot over medium heat. Add the sliced onions and salt, toss to coat, then cover the pot for 3 to 4 minutes to help them start sweating.

Step 2: Uncover and cook the onions for about 40 to 45 minutes, stirring every 8 to 10 minutes and reducing the heat to medium-low halfway through. This is the step that actually builds the soup’s flavor, don’t rush it. The onions should turn a deep caramel color, not just soft and translucent.

Step 3: While the onions cook, brush the baguette slices with olive oil on both sides. Place them on a baking sheet and bake at 350°F for about 10 minutes per side, until crisp. Set aside.

Step 4: Once the onions are deeply golden, add the garlic and thyme and stir for 1 to 2 minutes, until fragrant. Sprinkle the flour over the onions and stir, letting it toast for about a minute.

Step 5: Add the beef broth, bay leaf, and pepper, scraping up any browned bits from the bottom of the pot. Bring to a boil, then lower the heat and simmer uncovered for 10 minutes.

Step 6: Stir in the vinegar and taste. Adjust the salt and pepper as needed, then remove the bay leaf.

Step 7: Preheat the broiler, or set the oven to 475°F. Ladle the soup into oven-safe bowls, leaving about 1/2 inch at the top. Float 2 toasted baguette slices on top of each bowl, then cover with grated Gruyère. Place the bowls on a baking sheet and broil until the cheese is golden and bubbling, watching closely so it doesn’t burn.

Costco French Onion Soup Recipe Tips

• Don’t shortcut the caramelization. Onions that only cook for 10 or 15 minutes will taste sweet but flat, the deep flavor in real French onion soup comes from the full 40 plus minutes.
• Toast the bread separately before it goes on the soup. Bread that goes straight from raw into the broth turns mushy instead of holding its shape under the cheese.
• A small amount of flour toasted with the onions gives the broth a bit of body without making it feel thickened. Skip it and the soup will taste thinner than it should.
• The splash of vinegar at the end matters more than it seems like it should, it cuts through the richness and balances the sweetness from the onions.
• If your broiler runs hot, keep the bowls on a lower oven rack and watch them closely. Gruyère browns quickly and can go from golden to burnt in under a minute.

What Pairs Well With This Recipe?

A bowl of this soup makes a meal for any dinner on its own with a side salad, but it also works well as a starter before something heartier like Morton’s Steakhouse Chicken Christopher.

If you’re feeding a crowd, it pairs nicely alongside Popeyes Jambalaya Recipe for a spread with more variety on the table.

Frequently Asked Questions