01 - Place cubed potatoes in a large pot with salted water. Bring to a boil and cook until fork-tender, approximately 15 minutes. Drain thoroughly and return potatoes to the warm pot.
02 - Add butter and milk to the drained potatoes. Mash thoroughly until completely smooth and creamy with no lumps remaining.
03 - Heat a skillet over medium heat. Add shredded cabbage and sauté until tender, about 4 minutes. Add sliced scallions and continue cooking for 1 additional minute until fragrant.
04 - Stir the sautéed cabbage and scallions into the mashed potatoes. Season with salt and pepper. Allow mixture to cool completely to room temperature for easier handling.
05 - Scoop approximately 2 tablespoons of cooled colcannon mixture. Flatten slightly in your palm, place one cheddar cube in the center, and wrap potato mixture around cheese to enclose completely. Shape into a smooth ball. Repeat with remaining mixture.
06 - Roll each ball in flour to coat lightly, shaking off excess. Dip in beaten egg, allowing excess to drip off. Press into panko breadcrumbs to coat evenly on all sides.
07 - Heat 2 inches of vegetable oil in a deep skillet or pot to 350°F. Fry balls in batches, turning occasionally, until golden brown and crispy, 2 to 3 minutes per batch. Remove with a slotted spoon and drain on paper towels.
08 - Serve hot while cheese center remains melted and gooey for optimal texture and flavor.