Slow Cooker Bourbon French Onion Soup

4 large onions (3-4 lbs)
4 cups of beef stock (homemade or butcher-made recommended, or use low-sodium store-bought)
4 cups of chicken broth (homemade or butcher-made recommended, or use low-sodium store-bought)
114g (1 stick) of butter
1 cup of bourbon
1 tablespoon of brown sugar
1 tablespoon of granulated garlic
1 tablespoon of onion powder
1 tablespoon of MSG (optional)
1 tablespoon of dried oregano
1 sprig of rosemary and thyme
Salt and pepper to taste
Toasted French bread
Cheese of your choice (thin provolone and grated Gruyère work well)