Mix together all the ingredients for the mincemeat in a small bowl and set aside.
To make the pastry, rub the butter into the flour, then mix in the caster sugar and a pinch of salt.
Combine the pastry into a ball and knead it briefly - the dough will be quite firm.
Preheat the oven to 200C/fan 180C. Line a 12-hole shallow muffin tin, by pressing small walnut-sized balls of pastry into each hole. Fill with a generous amount of the mincemeat, then taking slightly smaller balls of pastry than before, pat them out between your hands to make round lids, big enough to cover the pies - you can cut stars out of the lids at this point for a decorative twist.
Top the pies with their lids, pressing the edges gently together to seal. Brush the top of the pies with the egg wash and bake for 20 mins until golden. Leave to cool in the tin for 5 mins, then remove to a wire rack.