First make the pastry: put the flour and salt in a large bowl and add the cubes of butter. Use your fingertips to rub the butter into the flour until you have a texture that resembles coarse breadcrumbs with no large lumps of butter remaining.
Using a knife, stir in just enough of the cold water to bind the dough together. Wrap the dough in cling film and chill for 30 minutes before using.
Preheat the oven to Gas Mark 4, 180°C, fan 160°C.
Roll out the chilled pastry dough to fit a 20cm (8in) pie dish. Place a piece of nonstick baking paper on the pastry and pour rice or baking beans on top to weigh it down. Bake blind in the preheated oven for 10 minutes, then remove the paper and beans and cook for a further 5 minutes until pale gold and sandy to the touch. Leave the oven on.
Make the filling: put the apple slices in a bowl and stir in the sugar, flour and cinnamon.
Make the crumble topping: sift the flour into a bowl and stir in the butter. Using your fingertips, rub the butter into the flour, until the mixture resembles breadcrumbs. Stir in the oats and sugar.
Tip the apple filling into the pie case and top with the crumble. Bake in the over for 30-40 minutes, until the crumble is crisp and golden, and the apples are soft underneath.
*Inspired by Emily B. featured in the Realfood Cookbook
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