Preheat the oven to 180C/350F/gas 4.
Grease the tart tin with butter.
To make the pastry sift the flour and salt into the mixing bowl or food processor bowl.
Add the butter and lard and then rub it in (or process if using a food processor) until the mixture resembles fine breadcrumbs.
Place the egg yolk in the cup and add the ice cold water and whisk together.
Add to the pastry mix and bring together to make a dough adding more water if the dough is too dry. If using a processor add the egg mixture and whizz until the mixture forms a ball of dough.
Wrap in clingfilm and place in the fridge for 30 minutes.
Remove the pastry from the fridge and place on a lightly floured work surface. Roll out the pastry and line the tart tin with it.
Arrange a layer of apples on the bottom of the pastry base, then add a layer of onions and sprinkle with some of the sage and spice. Season well.
Build up with alternate layers until you’ve used up all your filling ingredients, then dot the top with the clotted cream.
Cook in the oven for about 1 to 1¼ hours. Keep watching the pie for the first half an hour to check that the onion doesn’t start catching. You want the onions to brown rather than go black! As soon as any of the onion starts to darken too much put a sheet of kitchen foil over the top.
Remove the pie from the oven and allow to cool before removing the tart tin and placing on a serving dish.
