In a saute pan over medium high heat carmelize all the onions in the butter using the wine in splashes to deglaze the pan intermittently. This should take about an hour.
In stock pot on medium heat, simmer the beef stock (I used my own) and beef bone broth (my own) and add in the carmelized onions.
Heat the oven to 350. Tear a few slices of sourdough bread into pieces that will fit into your oven safe soup bowls. Either lightly brush them with a little butter or lightly spray them with oil. Coat both sides and toast in the oven turning once.
When the toast is done, ladle soup into the soup bowls, top with a toasty crouton, and then cheese. Place the bowls on a baking sheet and heat in the oven until the cheese is melted, about 15 minutes. Serve straight from the oven.