Chop up the potatoes and nuke in boiling water for about 5 minutes, drain when done. Meanwhile, chop up your onion and a can of corned beef (optional: add a chopped up carrot for veg - if you're entertaining a lady).
Mix the cooked potato, onion and corned beef in a casserole dish. Stir together the ketchup and stock and then pour into the casserole on top of the rest.
Cover the casserole and bake at about 400 F for about 20 min, then uncover and cook for about another 15 min until good and brown on top.
Serve with bread, more ketchup and beer.