Cook the potatoes for 25 minutes in a pan of lightly salted water, then drain, peel and dice.
Place them in a bowl with 55g of the butter and mash until smooth.
Meanwhile, place the cabbage, water and remaining butter in a large saucepan and cover. Cook gently for 10 minutes or until tender drain the water and mix the cabbage and mashed potato together.
Heat half the oil in a frying pan. Add the onion and SPAM® classic and cook, stirring occasionally until the SPAM® classic has browned. Add the potato and cabbage mixture and press down with the back of a wooden spoon to make a flat, even shape.
Cook over a medium heat for 15 minutes until golden brown on the underside and place on a large plate. Add the remaining oil and cook again on the other side for 10 minutes.