01 - Boil the cubed potatoes in salted water until fork-tender, approximately 15 minutes. Drain thoroughly and return to the cooking pot.
02 - Add butter and whole milk to the drained potatoes. Mash until completely smooth and creamy, ensuring no lumps remain.
03 - Heat a skillet over medium heat. Sauté shredded cabbage until tender, about 4 minutes. Add sliced scallions and continue cooking for 1 additional minute.
04 - Fold the sautéed cabbage and scallions into the mashed potatoes. Season with salt and pepper. Allow mixture to cool completely to room temperature.
05 - Scoop approximately 2 tablespoons of cooled colcannon mixture. Flatten in palm, place one cheddar cube in center, and enclose completely with potato mixture. Shape into smooth balls. Repeat with remaining ingredients.
06 - Coat each ball in flour, shaking off excess. Dip in beaten egg, allowing excess to drip off. Roll in panko breadcrumbs, pressing gently to adhere coating evenly.
07 - Heat 2 inches vegetable oil to 350°F in a deep skillet or pot. Fry balls in batches for 2 to 3 minutes, turning occasionally, until golden brown and crispy. Drain on paper towels.
08 - Serve hot while cheese remains melted and stretchy for optimal texture and flavor experience.