Mix the eggs, flour, milk, mustard and some salt and pepper together with a whisk, beating out any little lumps of flour. It should be the consistency of double cream, no thinner. Leave to rest for 15 minutes.
Cut the skin from each sausage and peel off. Wrap each skinned sausage in the prosciutto or whatever you are using.
Put the dripping or lard in a 28×21 cm roasting tin and put in the oven until it is smoking.
Pour the batter into the roasting tin then arrange the sausages in it. Bake for 25-30 minutes until puffed and golden.
Serve with an onion gravy- Nigel recommends his Browned Onion and Madeira Gravy.