Set aside 1½ tbsp of the beaten egg to use as a glaze later.

Add the remaining egg to the cold water and mix with a fork.

Sift the flour and salt into a large mixing bowl.

Coarsely grate the lard and butter into the flour, dipping them into the flour now and then to stop sticking to the grater. Rub the fats into the flour until the mixture resembles fine breadcrumbs.

Tip in the egg and water mixture and stir with a round bladed knife to start bringing the dough together then switch to your hands.

Transfer to a lightly floured surface and gently knead just enough to bring together into a smooth, elastic dough.

Cut off one quarter of the dough (use scales for accuracy) then briefly knead each piece into a smooth ball.

Wrap each dough ball in cling film and chill in the fridge for 1 hour.

Put the olive oil and butter in a frying pan over medium heat.

Skin the onions and chop finely.

When the pan is hot, tip in the onion and season with a little salt, a good grind of black pepper, plus the dried sage.

Cook, stirring often, until the onion is soft and starting to brown (12-15 min).

Remove and discard any rind from the bacon. Chop the bacon finely (or use a mincer).

Put the chopped bacon and sausage meat into a large mixing bowl.

Grate the apple onto a plate or board then take handfuls and squeeze out as much juice as possible (apple juice in the filling will make the pie too wet).

Transfer the squeezed apple to the bowl with the bacon and sausage meat, along with the cooked onion and any fat from the frying pan.

Season again with a little salt and black pepper.

Mix the pie filling together so that everything is well combined: using your hands and squeezing the mixture together is best.

Recommended: take a teaspoon of the mixture, shape into a ball or patty and cook in the frying pan. Cool a little, then taste and add more seasoning to the mixture if needed.

Preheat the oven to 200 C / 180 C Fan / Gas 6.

Butter a round 18 cm / 7 in diameter springform cake tin that's 7 cm / 2½ in deep

On a lightly floured surface, roll out the large piece of dough so that it fits the tin and comes up just above the rim.

Pack the pie filling into the pastry case, pressing down to prevent any air pockets, and smooth the top.

Cut off excess pastry so that it's flush with the top of the tin.

Take the small piece of dough and roll into a circle 18 cm in diameter.

Brush a little of the reserved beaten egg on the pastry around the edge of the tin.

Place the circle of dough on top, press down to seal, then pinch together all the way around.

Brush all over with a light glaze of beaten egg (save the rest, you'll need it later), then poke one or two holes in the top of the pastry lid.

Put the tin on a baking tray (to catch any escaping juices) and transfer to the oven.

Bake for 30 minutes.

Take the pie out of the oven and reduce the temperature to 160 C / 140 C Fan / Gas 3.

Brush with another layer of beaten egg then return to the oven.

Bake for a further 1½ hours.

Tip: if the pastry is browned before the time is up, cover loosely with foil. Remove the foil for the final 10 minutes of cooking.

Take the pie out of the oven and put on a wire rack to cool, but do not remove it from the tin at this stage. Leave for 1 hour.

Unlock the spring on the tin and lift the sides off.

Carefully lift the pie off the base of the tin and place on the wire rack until cold.

Store in the fridge in an airtight container or wrapped in foil.

Best left until the next day before cutting into.

Should keep for 5 days.