Slow Cooker French Onion Soup

<p>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.<br />
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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.<br />
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About 10 minutes before serving, set oven rack about 8 inches from the heat source and preheat the oven&#39;s broiler. Arrange bread slices on a baking sheet.<br />
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Broil bread slices until toasted, 1 to 2 minutes per side.<br />
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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 European Cheese Mixture (separate recipe) mixture per serving.<br />
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Place filled bowls onto a baking sheet and broil until cheese topping is lightly browned and bubbling, about 2 minutes.<br />
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NOTE: This recipe can be done completely in a slow cooker.&nbsp; Instead of carmelizing onions in a pan, add onions to slow cooker with butter, sugar, garlic, and salt.&nbsp; Cook for 6 hours on high. Then, continue with recipe by adding remainder of ingredients.<br />
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