French Onion Soup

I was craving French onion Soup and so I made some instead of going out to get any, which can be hard to find plus has tons of salt and who knows what other ingredients I don't need.
This soup is so good slightly rich very warm and cheesy too. Mmmmm

6 servings

Ingredients
3 tablespoons unsalted butter
3 1/2 pounds red onion, thinly sliced with a slicer is best you can use a mix of onions
2 teaspoons chopped fresh thyme or 1 tablespoon dried
4 cloves garlic, minced
1 cup dry white wine or beef or any broth
6 cups chicken broth, homemade or low-sodium
1 teaspoon sea salt plus more to taste
1 tablespoon red wine vinegar
Freshly ground black pepper
Six 1/2-inch slices baguette (French bread), toasted
12 ounces Gruyere and swiss cheese, shredded (about 3 cups together)

Directions
In a large soup pot or Dutch oven, melt the butter over medium heat. Add the onions, stir to combine with the butter, cover, and cook for 30 minutes, stirring occasionally. Remove the cover; increase the heat to medium-high and cook, until the onions are brown and caramelized, about 30 minutes. (Stir the onions frequently toward the end of this stage in the cooking, so they do not scorch or burn.) Add the thyme and garlic, saute for 2 to 3 minutes more. Pour in the wine and scrape up the browned bits from the bottom of the pan with a wooden spoon; simmer until the wine or broth, is reduced by about half. Stir in the 6 cups of broth and salt and bring to a gentle simmer. Cover, and cook for 30 minutes. Add the red wine vinegar if using, and season with pepper to taste. (The soup can be made to this point a day ahead and refrigerated.)

When ready to serve preheat the broiler. Heat the soup and divide it evenly among 6 heat proof crocks or bowls. Top each soup with a slice of the bread and about 1/2 cup of the cheese. Place the bowls on a sheet pan and broil until the cheese is bubbly and brown. Careful removing as soup will be very hot, serve bowls on plates for safety and serve with bread.