In a large bowl, mix together the potato, parsnip, chives, egg whites, cornstarch, 1 teaspoon salt, and plenty of black pepper.

Heat half the butter and oil in a large frying pan over medium-high heat. Use your hands to pick out portions of about 2 tablespoons of the latke mix, squeeze firmly to remove some of the liquid, and shape into thin patties about ¾-inch thick and 3 ¼-inches in diameter. Carefully place as many latkes as you can comfortably fit in the pan, push them down gently, and level them with the back of a spoon.

Fry over medium-high heat for 3-4 minutes on each side. The latkes need to be completely brown on the outside. Remove the fried latkes from the oil, place on paper towels, and keep warm while you cook the rest. Serve immediately with sour cream on the side.