01 - Place the grated raw potatoes in a clean kitchen towel and firmly wring out as much moisture as possible.
02 - In a large mixing bowl, combine the drained grated potatoes, mashed potatoes, all-purpose flour, baking powder, salt, and ground black pepper. Mix thoroughly until well incorporated.
03 - Gradually stir in the whole milk and the lightly beaten egg until a thick, cohesive batter is formed.
04 - Heat 1 tablespoon of unsalted butter and 1 tablespoon of vegetable oil in a large nonstick skillet over medium heat until shimmering.
05 - Working in batches, carefully drop heaping tablespoons of batter into the preheated skillet, gently flattening each mound to form a pancake. Cook for 3 to 4 minutes per side, or until golden brown and crispy.
06 - As needed for subsequent batches, add more butter and oil to the skillet to maintain optimal cooking conditions for the remaining batter.
07 - Transfer the cooked boxty to a plate lined with a paper towel to drain any excess oil. Serve immediately while hot.