Mix the flour, 1 egg, the milk and a pinch of salt in a jug or bowl. Set aside for 30 mins, or up to 3 hrs. Mash together the mustard, cream and cheese in another bowl. Heat the oven to 200C/180C fan/gas 6, and line two baking trays with baking parchment or foil.
Melt the butter in a large frying pan, then once foaming, add enough batter to just cover the pan, swirling it to cover the surface in a thin layer (pour any excess back into the batter bowl). Cook until the surface is set and the underside is browning, carefully flip and cook for another minute or 2, then take off the heat.
Spoon a quarter of the cheese mixture onto the middle of the pancake, using the spoon to create space in the centre to hold an egg. Crack one into the space and lay a few pieces of ham around the edges. Fold each side of the pancake in towards the centre to make a square. Cook in the pan for another 30 secs-1 min, then transfer to a baking tray. Repeat with the rest of the pancakes, then bake for 6-7 mins until the egg whites are set. Serve with fried mushrooms or wilted spinach, if you like.