01 - Wrap grated raw potatoes in a clean kitchen towel and squeeze firmly to remove excess liquid until potatoes feel dry to the touch.
02 - Combine grated potatoes, mashed potatoes, flour, baking powder, salt, and pepper in a large mixing bowl.
03 - Pour milk and melted butter into the potato mixture. Stir until just combined—the batter should remain thick and spoonable.
04 - Warm vegetable oil in a large non-stick skillet over medium heat until the surface shimmers slightly.
05 - Drop heaping tablespoons of batter into the hot pan. Flatten each portion with the back of a spoon to create rounds approximately 1/2 inch thick.
06 - Fry for 3 to 4 minutes per side until both surfaces develop a deep golden color and crisp texture. Add more oil between batches as necessary.
07 - Transfer cooked boxty to paper towels to absorb residual oil while you finish remaining batches.
08 - Plate warm pancakes topped with a generous dollop of sour cream and a sprinkling of fresh chives.