First, make the shortcrust pastry. Place the flour into a cold mixing bowl, then cut in the lard or butter and rub between your fingertips until the mixture resembles fine breadcrumbs (do this as quickly as possible so that you keep the pastry as cool as possible). Add a pinch of salt then just enough ice cold water to bind the mixture into a firm pastry dough. Wrap in clingfilm and place in the fridge to chill for 30 minutes.
Meanwhile, in a saucepan of boiling water, add the potatoes and cook until tender. Remove from the heat and drain. Combine with the other ingredients, except the egg, and place in the fridge along with the pastry.
Preheat the oven to 180 C / Gas 4.
Return the filling to the heat and warm through. Stir to ensure that all the ingredients are well mixed and the flavours have infused throughout.
Remove the pastry from the fridge and on a floured work surface, turn out the pastry and roll out to a 5mm thickness. Using an inverted side plate, cut out 12 to 14 circles then divide the filling among the circles. Fold the pasties over then press the edges together with your fingers to seal. Place on to a baking tray then lightly brush with egg.
Bake in the preheated oven for 30 to 40 minutes, or until the pasty is golden brown. Remove from the oven and serve warm or cold.