Sweet-Potato Soup with Prosciutto Crisps... Sweet-Potato Soup with Prosciutto Crisps Ingredients 1 1/2 tablespoons unsalted butter 1 large leek (white and light green parts only), thinly sliced, rinsed, and drained 2 small garlic cloves, minced 2 pounds orange sweet potatoes (about 2 large sweet potatoes; often labeled "yams"), peeled and cut into roughly 1-in. pieces