Put lard and margarine into a bowl, sift in the flour and rub ingredients together. Add 3 tablespoons of water, mix with a knife then use hands to blend. Wrap in cling film and chill in fridge for 30 minutes.
Preheat the oven to 200 C / Gas 6. Grease a baking tray.
Divide the pastry into 3. Dust your work surface with flour and roll each portion into a rectangle about 30cm long.
Divide the meat into 3. Roll each portion into a tube shape about 25cm long. Place each portion onto the pastry and brush milk along the edges. wrap one side of pastry onto the sausage, then the other so there are no gaps. Cut a few slits on each one and brush with milk.
Bake for 25 minutes. Do not open the oven door until at least 20 minutes have passed.