Mix mashed potatoes, flour, onion, 1 egg, green onions, black pepper and salt together in a bowl until batter consistency.

Heat vegetable oil in a skillet over medium heat. Drop 4-inch circles of batter into hot oil. Cook until golden brown, about 5 minutes per side. Remove with a slotted spoon and drain on paper towels. Repeat with remaining batter.

In a separate bowl, mix mayo, sour cream, zest, lemon, parsley, 1 egg yolk, salt and pepper