Recipe: Sweet Potato Gratin with Caramelized Onions

Name: Recipe: Sweet Potato Gratin with Caramelized Onions
Ingredients: 2 tablespoons unsalted butter; 2 medium onions, peeled and sliced into thin half moons; 3 pounds sweet potatoes or yams (3 to 4 large potatoes); Kosher salt and freshly ground black pepper; 4 cloves garlic, minced; 1/4 cup fresh sage leaves, finely chopped; 1/4 teaspoon chipotle pepper powder ( optional ); 1 cup heavy cream; 1 tablespoon unsalted butter; 2 tablespoons finely chopped sage leaves; 1/2 cup fine dried breadcrumbs; 1/2 cup grated Parmesan; Olive oil