Sweet Potato–Apple Rosti With Leafy Greens Sour Cream

Name: Sweet Potato–Apple Rosti With Leafy Greens & Sour Cream
Ingredients: 2 pounds sweet potatoes, washed but not peeled; 2 apples, cut from the core but not peeled; 1/4 cup cornstarch; 1/4 cup (2 ounces) unsalted butter (or substitute neutral oil); Salt and freshly ground black pepper; 5 sprigs dill, roughly chopped; 4 ounces baby kale, spinach, or arugula; Extra-virgin olive oil; Freshly squeezed lemon juice or vinegar; 4 ounces sour cream