Onion Sweet Potato Gratin - What's Cooking Wednesday

A classic side dish, gratins are simply delicious. This one uses sweet potatoes and onions. Ingredients Nonstick cooking spray 2 tablespoons olive oil 5 cups sliced onion 3 tablespoons dark brown sugar 1/4 teaspoon cayenne pepper 1/3 cup butter 3 tablespoons all-purpose flour 2 cups half-and-half 1 teaspoon Dijon mustard 1/2 teaspoon smoked paprika 1/2 teaspoon ground black pepper 1 1/2 teaspoons salt 3 pounds peeled, very thinly sliced sweet potato 2 cups grated Parmesan 2 tablespoons chopped fresh parsley, optional Preparation