01 - Wrap grated raw potatoes in a clean kitchen towel and squeeze firmly to remove excess moisture.
02 - Combine grated raw potatoes, mashed cooked potatoes, flour, baking powder, salt, and pepper in a large bowl. Mix thoroughly.
03 - Gradually pour in milk while stirring until batter reaches a thick, spoonable consistency.
04 - Heat 1 tbsp butter and 1 tbsp oil in a large non-stick skillet over medium heat until butter melts and bubbles.
05 - Drop heaped spoonfuls of batter into the pan, gently flattening each to form pancakes about 1/2 inch thick.
06 - Cook for 3-4 minutes per side until golden brown and crisp. Add more butter and oil between batches as needed.
07 - Transfer cooked boxty to paper towels to drain. Serve immediately with sour cream and fresh chives.