Combine both flours, the butter and a pinch of salt in the bowl of a food processor and blitz to a fine crumb. Add cold water 1 tbsp at a time (4-5 tbsp), pulsing until the mix starts to cling together. Tip out and knead with your hands (add more water if required) to make a pliable pastry dough. Split in half and flatten each portion. Wrap and refrigerate for at least 1 hr.
Remove a disc of pastry from the fridge, unwrap and, on a generously floured surface, roll it out to a large, circle, wider than the pie dish. Transfer to a floured baking sheet and chill for about 10 mins. Repeat with the remaining disc.
Heat the oven to 180C/160C fan/gas 4. Stone and quarter the peaches. Cut each in two, and toss in a bowl with the lemon juice, cornflour, vanilla extract, sugar, honey and raspberries. Add the butter in small pieces.
Using a floured rolling pin, drape one of the pastry sheets across a 24cm pie dish. Let it sink in and, holding the edges, lift and tuck into the corners. Prick the pastry all over and fill with the peach mixture.
Drape the second pastry sheet over the filling. Press together the top and bottom crusts, crimping with your fingers to seal, and trim off any excess. Cut three 8cm slits across the top crust, brush with the beaten egg and sprinkle over the demerara sugar. Bake for 55 mins to 1 hr until the crust is deeply golden and the filling is bubbling out. Cool for about 10 mins before serving with cream or vanilla ice cream.