30g unsalted butter
6 Granny Smith apples, peeled, cored, sliced
150g caster sugar, plus extra to sprinkle
1 bunch rhubarb, washed, sliced
1/2 teaspoon ground cinnamon
1 tablespoon milk
Thick cream or custard, to serve
300g plain flour
150g unsalted butter, cubed
To make the pastry, place the flour and butter in a food processor and process until the mixture resembles fine breadcrumbs. Add the egg and 1-2 tablespoons chilled water and process until it comes together to form a smooth ball. Wrap in plastic wrap and refrigerate for 30 minutes.
Preheat oven to 180°C.
Melt the butter in a large frying pan. Add the apples and sugar and cook for 2-3 minutes over low heat. Add the rhubarb and cinnamon and cook for a further 2-3 minutes until the fruits are just starting to soften. Transfer into a 3-litre (6-cup capacity) pie dish and set aside to cool.
Roll out the pastry on a lightly floured work surface and cut a 1 1/2cm-wide strip of pastry. Press it around the rim of the pie dish and brush with a little water. Cover with remaining pastry, then trim the edges. (This method helps stop the pastry lid shrinking.) Pinch the pastry together to seal, brush with milk and scatter with the extra caster sugar.
Bake the pie for 35-40 minutes until the pastry is golden. Serve hot or warm with thick cream or custard.