Butter a 30cm deep roasting dish. Spread the butter on the holey sides of each crumpet. Put into the dish and put a slice of ham between them.
Gently heat the milk and cream in a medium saucepan on low heat. Once steaming, set aside to cool slightly. Whisk the eggs, most of the grated cheese, mustard, chives and plenty of salt and pepper in a large bowl. Stream in the milk, whisking as you go. Once totally combined, ladle it over the crumpets, soaking them will in the custard mix.
Leave to soak in the fridge for 30 mins. Heat the oven to 180C/160C fan/gas 5. Sprinkle the remaining cheese on top of the bake. Bake for 35-40 mins until golden, puffed up and set around the edges. Leave to cool for 5 mins before serving with some more chives, if you like.
