Parsnips add a tinge of sweetness to these latkes; for a delicious twist, serve them with pear sauce made in the usual manner of applesauce.
In a large bowl, combine onion, orange zest, salt, cayenne, and black pepper. Add eggs, and stir until incorporated. Stir in flour until mixture is smooth. Add parsnips and potato, and toss until combined and evenly coated.
Fill a large, heavy-bottom skillet with about 1/2 inch oil. Place over medium heat until oil is almost smoking. (To test, drop a small bit of batter into the skillet; the oil should sizzle upon contact.)
Working in batches so as not to crowd skillet, carefully spoon about 2 tablespoons batter into oil for each pancake. Lightly tamp down to flatten. Cook until golden on each side, 2 to 3 minutes, turning once. Using a slotted spatula, transfer to drain on a paper-towel-lined wire rack, and repeat with remaining batter. Serve immediately with applesauce or pear sauce and sour cream, if desired.