Peach and tarragon crumble pie

1 Preheat the oven to 220 ̊C, gas mark 7, and put a baking tray on the bottom shelf to heat up. Mix 125g granulated sugar, the plain flour, cinnamon and a pinch of salt in a large mixing bowl. Add the butter and, using your fingers, rub everything together until you have coarse crumbs; set aside.
2 Line a 23cm pie dish with the pastry, cutting and piecing it together if need be, then trim the edges. Crimp the edges with your fingers, then chill until the filling is ready.
3 Roughly chop the peaches and put them in a bowl with the tarragon, cornflour and remaining 125g granulated sugar; stir together. Spoon the mixture into the pastry case, then evenly spoon over the crumble topping. Put on the baking tray in the oven and bake for 10 minutes, then reduce the temperature to 200 ̊C, gas mark 6, and bake for a further 40 minutes, until golden and bubbling (you may need to cover the pastry edge with foil if it starts to darken too much). Remove from the oven and leave to cool for at least 2 hours before serving with ice cream or warm custard, if liked.