5 large onions, sliced
4 tablespoons butter
1 tablespoon brown sugar
1 teaspoon finely chopped fresh thyme
1½ teaspoons salt
2 quarts beef broth, no sodium added
¼ cup sherry
1 French baguette, cut into 1-inch slices
8 ounces Gruyere cheese, sliced (can substitute with Swiss cheese if desired)
In a 6-quart slow cooker, add onions, butter, brown sugar, thyme and salt. Mix well and cook on low for 8 hours.
If you're around during the 8 hours, stir the onions every now and then, for even browning. This isn't necessary but suggested.
After 8 hours, mix well. Onions should be soft and brown.
Mix in beef broth and sherry. Cook on high for another hour.
Meanwhile, place Gruyere cheese on top of baguette slices and toast in oven until cheese is melted.
When soup is ready, serve in bowls. Top with 1 or 2 pieces of toasted bread directly on soup.
Pro tip: If you don't want to toast your bread and melt cheese in the oven, simply put the bread slices right on top of the soup in the slow cooker. Evenly spread Gruyere on top of the bread and cook on high for another 15 to 20 minutes, until cheese is melted.