Onion and Mushroom Soup

Name: Onion and Mushroom Soup
Ingredients: 2 tablespoons olive oil; 2 tablespoons butter; 8 onions cut in half pole to pole and sliced; 8 ounces mushrooms, sliced; 1 clove garlic, minced or put through a garlic press; 1/2 teaspoon sea salt; 3-4 turns of freshly-ground black pepper; 1 tablespoon flour; 1/2 cup dry sherry; 4 cups chicken stock (or low sodium chicken broth); 1/2 teaspoon dried thyme (or a few sprigs of fresh thyme; unfortunately my thyme is buried under about 8 inches of snow.); 1 tablespoon balsamic vinegar; 1 small baguette, cut into 1/2 inch slices; shredded Gruyere cheese