Preheat the oven to 180ºC/350ºF/Gas Mark 6. Rub a little butter inside a ramekin. Break up the slice of ham into the bottom. Crack the egg on top, then sprinkle the cheese over. Bake for 12–15 minutes.
Let it cool slightly and wrap a wet napkin around the outside of the ramekin for the children, in case it is too hot.