Slow Cooker French Onion Soup

Get ready for the most satisfying bowl of comfort you’ll ever make in your slow cooker. This French onion soup transforms humble ingredients into a rich, deeply flavorful masterpiece that’ll have everyone asking for seconds.

The magic happens as sweet Vidalia onions slowly caramelize over hours, developing an incredibly rich, almost candy-like sweetness that mingles with savory beef broth. Topped with crusty baguette and melted Gruyère cheese, it’s the definition of cozy sophistication.

Ingredients

For the Base:

• 2 lbs Vidalia onions, thinly sliced (about 8 cups)
• 1/4 cup unsalted butter, melted
• 1 1/2 tsp granulated sugar
• 1 1/2 tsp kosher salt
• 1/2 tsp black pepper, plus more for garnish
• 6 thyme sprigs, tied with kitchen twine
• 1 dried bay leaf
• 5 cups lower-sodium beef broth
• 1 Tbsp sherry vinegar

For Topping:

• 12 baguette slices (1/2-inch thick)
• 6 oz Gruyère cheese, shredded (about 1 1/2 cups)
• Fresh thyme leaves for garnish

Steps

1. Prepare the onions by combining 2 lbs sliced onions, 1/4 cup melted butter, 1 1/2 tsp sugar, 1 1/2 tsp salt, and 1/2 tsp pepper in a 6-quart slow cooker. Mix until every onion slice is coated. Add the tied thyme sprigs and bay leaf on top. The sugar helps with caramelization, while the salt draws out moisture.
2. Cover and cook on HIGH for 6-7 hours, stirring once at the 3-hour mark. The onions should turn a deep golden brown and reduce significantly in volume. They’re done when they’re uniformly caramelized with no light spots remaining.
3. Remove and discard the herb bundle and bay leaf. Add 5 cups beef broth and 1 Tbsp sherry vinegar. Cover and cook on HIGH for 30 minutes until piping hot (165°F/74°C).
4. Position oven rack 6 inches from broiler and preheat to BROIL (500°F/260°C). Ladle hot soup into 6 oven-safe ramekins placed on a rimmed baking sheet.
5. Top each ramekin with 2 baguette slices and 1/4 cup shredded Gruyère. Watch carefully while broiling for 2-3 minutes until cheese is melted and golden brown with some darker spots.
6. Garnish with fresh thyme leaves and additional black pepper. Serve immediately while the cheese is hot and stretchy.

Smart Swaps

• Use Swiss cheese instead of Gruyère (same amount)
• Replace beef broth with mushroom broth for vegetarian version
• Substitute white wine vinegar for sherry vinegar

Make It Diabetes-Friendly

• Reduce sugar to 1/2 tsp (saves 1g carbs per serving)
• Use thin-sliced cloud bread instead of baguette (reduces carbs by 15g per serving)
• Serve with a side salad to slow glucose absorption

Pro Tips

• Slice onions uniformly (1/8 inch) for even cooking
• Don’t skip the sugar – it’s crucial for proper caramelization
• Use room temperature cheese for better melting
• Let ramekins cool for 2-3 minutes before serving to avoid burns