01 - Wrap grated raw potatoes in a clean kitchen towel and squeeze firmly to remove excess liquid.
02 - Mix grated potatoes, mashed potatoes, flour, baking powder, salt, and pepper in a large bowl.
03 - Add milk and melted butter; stir until just combined. Batter should be thick and spoonable.
04 - Heat vegetable oil in a large non-stick skillet over medium heat.
05 - Drop heaping tablespoons of batter into pan; flatten to 1/2 inch thick rounds.
06 - Fry 3-4 minutes per side until golden brown and crisp. Add oil as needed between batches.
07 - Transfer cooked boxty to paper towels to drain.
08 - Serve warm topped with sour cream and fresh chives.