Rice potatoes. Whisk in butter, sour cream, and yolks. Fold in cheese and scallions. Season to taste. Chill for 1 hour.
Form into cakes 2 by 1 inch. Heat the oil and butter in a skillet on medium heat, until butter starts to foam. Gently place cakes in the pan and cook for approximately 3 minutes on each side or until golden brown.