Combine flour and salt in a bowl and rub in butter until it looks like breadcrumbs.
Add beaten egg to form a dough, shape into an oval 1cm deep, and chill for 30 minutes.
Boil the bacon joint in water for 45 to 60 minutes until cooked.
Fry sliced onion and garlic in butter until soft and golden-brown.
Drain the cooked bacon and allow it to cool.
Preheat your oven to 180°C.
Whisk cider, cream, mustard, sugar, herbs, and cornflour together and season.
Slice the cooled bacon joint into 5mm thick pieces.
Layer half the potatoes, onions, apples, and bacon in a greased 2 litre dish.
Pour half the cream mixture over the layers and repeat with remaining ingredients.
Roll pastry to 4mm thickness and place on top of the pie dish.
Glaze the pastry with leftover egg or milk.
Decorate with pastry scraps, cut a steam hole, and crimp the edges.
Bake for 45 minutes until the pastry is golden and the filling bubbles.