Pre heat the oven to 150°C, and lay the ham on a trivet of roughly cut onions and celery.
Place in the bottom of the oven and roast for 20 minutes plus a further 25 minutes per 500 g, making sure the core temperature reaches a minimum of 72°C.
Leave to cool a little before carving thinly, 5 mm or so thick.
Great served with some simple steamed heritage potatoes, good quality butter and Cusack's beer mustard.
