Place 3 large unpeeled potatoes in cold water, bring to a boil, and cook for about 40 minutes or until done. Test potatoes with a skewer to see when done. Place them in a bowl, then peel while hot.
Press the potatoes through a strainer while still hot. If potatoes are cool they will be sticky, making it difficult to pass them through the strainer.
Season with salt and pepper. Mix these ingredients with the mashed potato. Mix well, and cool.
Meanwhile, melt margerine in a frying pan then add flour.
Add the milk and stir until the sauce becomes creamy.
Wait until the sauce thickens, then add the canned corn and mix them well. Refrigerate the sauce in a bowl for several minutes.
Heat 1 tablespoon of olive oil in a frying pan. Add sauce and mix it with the mashed potato. Season with salt and pepper.
Form potato mixture into patties, and dredge patties in the flour until they are coated evenly, dip in beaten egg then coat evenly with panko.
Deep fry the korokke pieces until they are golden brown.
Place thinly sliced cabbage on a plate, place korokke pieces over it. Serve them with korokke sauce or mayonnaise.