Set a Dutch oven, or other large soup pot, over medium heat. Add the butter to melt.
1/2 cup salted butter
Add the onions to the pot and cook, stirring often, until they're a nice caramelized brown.
4-5 large sweet onions
Add the broth, sherry, sugar, flour, and Worcestershire to the pot then stir until everything's evenly combined. Add the remaining ingredients to the pot, except for the cheeses, and stir to combine.
8 cups beef broth, 1/4 cup cooking sherry, 1/2 tbsp sugar, 2 tbsp flour, 2 tsp Worcestershire sauce, 2 dried bay leaves, 2-3 sprigs fresh thyme, 1 12 oz pkg frozen egg noodles
Turn the heat up to high and bring the soup to a boil then immediately reduce the heat so that the soup's at a simmer. Cook for 30 minutes, just until the noodles are properly cooked.
Mix the cheeses together in a small bowl. Set aside.
1 cup shredded Swiss cheese, 1 cup shredded gruyere cheese
Ladle the hot soup into bowls and top each with some of the cheese blend. Let it rest until the cheese has melted on top.
Serve warm & enjoy!