Preheat oven to 450 degrees F (230 degrees C). Line a baking sheet with parchment paper.
Stir panko bread crumbs and melted butter together in a shallow bowl; set aside to moisten.
Stir mashed potatoes, stuffing, and turkey together in a bowl. Roll about 1 1/2 tablespoons turkey mixture into a ball or log shapes; dip into beaten egg, roll in panko bread crumb mixture, and place on prepared baking sheet. Repeat with remaining turkey mixture.
Bake in the preheated oven until golden and crisp, about 15 minutes.