Turn your crockpoot on high heat. Add in your onions, top with butter, balasamic, brown sugar, and garlic. Cook for 1-1 ½ hours, stir occasionally.
Onions are ready when they are caramel colored and very soft.
Pour in beer, and broth, add seasonings. Turn crockpot to low and let soup cook for 6-8 hours.
Place oven safe bowls on a baking sheet, fill with soup. Slice french bread on the diagonal and place one in each bowl of soup. Top each with a slice of provolone cheese.
Place under broiler for 2-3 minutes until cheese is bubbly and edges begin to brown.