French Pearl Onion Soup

Ingredients
1 (14.4 oz.) bag frozen pearl onions, thawed and drained
4 large yellow onions, peeled and thinly sliced
2 tablespoons unsalted butter
1 tablespoon extra-virgin olive oil
4 cloves garlic, minced
1 teaspoon dried sage
1 teaspoon dried thyme
1/2 tablespoon balsamic vinegar
1/2 cup preferred red wine
2 (32 oz.) containers beef stock
2 bay leaves
1/2 teaspoon kosher salt
1/4 teaspoon black pepper
2 cups Swiss or gruyere cheese, grated
Croutons:
1 loaf French bread
1/4 cup (1/2 stick) unsalted butter, melted
1/4 teaspoon garlic powder
1/4 teaspoon onion powder
Preparation