Heat the oven to Gas 3, 170°C, fan 150°C.
Melt the butter in a frying pan over medium heat and fry the ham on both sides for 2 minutes til brown. Arrange the ham in a baking dish and cover with the sliced potatoes. Season with salt and pepper, sprinkle over the onion and pour the milk over the top.
Cover the dish with foil and bake for 1 hour.
Remove the foil and sprinkle the grated cheese on top of the potatoes. Return to the oven for 30 minutes longer until the cheese has melted and turned golden. Serve at once.
Serve with a green salad and some crusty bread for a comforting supper dish.
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