Slow Cooker French Onion Soup Recipe

Heat butter in a large heavy pot over medium-high heat; cook and stir onions until they become translucent about 10 minutes. Sprinkle onions with sugar; reduce heat to medium. Cook stirring constantly until onions are soft and browned at least 30 minutes. Stir in garlic and cook until fragrant about 1 minute.

Stir sherry into onion mixture and scrape bottom of pot to dissolve small bits of browned food from the pot. Transfer onions into a slow cooker and pour in beef broth. Season to taste with sea salt; stir in thyme and bay leaf. Cover cooker set on High and cook 4 to 6 hours. If desired set on Low and cook 8 to 10 hours.

About 10 minutes before serving set oven rack about 8 inches from the heat source and preheat the oven's broiler. Arrange bread slices on a baking sheet.

Broil bread slices until toasted 1 to 2 minutes per side.

Combine Gruyere Emmental Parmesan and mozzarella cheeses in a bowl tossing lightly. Fill oven-safe soup crocks 3/4 full of onion soup and float a bread slice in each bowl. Top with about 2 tablespoons of cheese mixture per serving.

Place filled bowls onto a baking sheet and broil until cheese topping is lightly browned and bubbling about 2 minutes.