onion soup recipe

½ cup unsalted butter 4 onions, sliced 2 garlic cloves, chopped 2 bay leaves 2 fresh thyme sprigs Kosher salt and freshly ground black pepper 1 cup red wine (about ½ bottle) 3 heaping tablespoons all-purpose flour 2 quarts beef broth 1 baguette, sliced ½ pound Gruyere cheese, grated