Slow Cooker French Onion Soup

Recipe View Gather all ingredients.

Recipe View Melt butter in a large, heavy-bottomed pot over medium-high heat. Add sliced onions and cook, stirring occasionally, until softened and translucent, about 10 minutes.

Recipe View Sprinkle onions with sugar and reduce heat to medium-low. Continue to cook, stirring frequently, until onions are deeply caramelized and a rich golden-brown color, at least 30 minutes. Stir in minced garlic and cook until fragrant, about 1 minute.

Recipe View Pour sherry into the pot with the onion mixture, scraping up any browned bits from the bottom of the pot to deglaze it.

Recipe View Transfer the caramelized onion mixture to a slow cooker and pour in beef broth. Season with sea salt, thyme, and bay leaf.

Recipe View Cover and cook on Low heat for 8 to 10 hours, or on High heat for 4 to 6 hours.

Recipe View About 10 minutes before serving, preheat oven broiler. Place an oven rack about 8 inches from the heat source. Arrange baguette slices on a baking sheet and broil until toasted and golden brown, about 1 to 2 minutes per side. Watch carefully to prevent burning.

Recipe View In a small bowl, lightly toss together Gruyère, Emmental, Parmesan, and mozzarella cheeses.

Recipe View Ladle the onion soup into oven-safe crocks or bowls, filling each about 3/4 full. Float a toasted baguette slice on top of each bowl of soup.

Recipe View Top each bowl with about 2 tablespoons of the cheese mixture.

Recipe View Place the filled bowls on a baking sheet and broil until the cheese topping is melted, bubbly, and lightly browned, about 2 minutes. Keep a close eye on the bowls to prevent burning.