6-7 Decent sized potatoes
Grated Cheese
Tin of cooked ham (use half and chop it up)
Chopped medium onion
knob of butter

Boil the potatoes in water until cooked.
Melt the butter in a frying pan on a low heat and cook teh chopped onion for a few minutes before adding the ham. Season with lots of pepper (and salt if the ham isnt salty)
Mash the potatoes

Layer into a ovenproof dish as follows
Potato
Ham and onions
Cheese
Potato
Ham and onions
Cheese
Potato

Is also nice if you sprinkle crushed smokey bacon crisps on top and then stick it in the oven for 30 mins at 180-200oC.