Shred sweet potatoes, peeled, and Yukon Gold potatoes, peeled, into large bowl. Stir in egg whites, all-purpose flour, salt, and pepper.
Heat peanut oil in large skillet until it is barely smoking. Drop batter by heaping tablespoonfuls into skillet. Cook pancakes over medium-high heat 4 to 6 minutes on each side, or until golden-brown. Drain on paper towels and serve immediately.