How to Make It
Preheat the oven to 400°. Wrap the potatoes individually in aluminum foil and bake for 45 minutes, or until they are fork tender. Remove the foil. When the potatoes are cool enough to handle, peel them with a paring knife. Trim off the rounded sides and cut the potatoes into 1-inch cubes. Season with salt and pepper.
Put the flour, eggs and panko in 3 shallow bowls. Dredge the potato cubes in the flour, shaking off any excess, then dip in the egg and coat thoroughly with the panko. Spread the cubes on a baking sheet.
In a large, heavy pot, heat 2 inches of the oil to 360°. Line a plate with paper towels. Working in batches, fry the potatoes until golden brown, about 2 minutes. Using a slotted spoon, transfer the potatoes to the paper towel–lined plate to drain. Serve with the tonkatsu sauce for dipping.
Like panko, tonkatsu, an intensely flavored Japanese steak sauce, can be found at supermarkets and Asian groceries. When making these croquettes, it's best to use one hand for dredging the potatoes in the dry ingredients and the other for dipping them in the egg.