PIE DOUGH

1. Place flour, sugar and salt into a large bowl. Cut butter into chunks, and add to the flour. Toss lightly to coat. Working quickly, using a pastry blender or  your fingers,  cut the butter into the flour mixture until there are only pea-sized chunks left. You want a few lumps of butter remaining to keep the pastry nice and tender.
2. Combine ice, water and cider vinegar in a bowl. Sprinkle a few tablespoons of the ice water into the flour and butter mixture, and using a stiff spatula or your hands, mix in well. Continue adding water a tablespoon at a time ( I normally need about 8-10 tbsp) until you have a dough that holds together well, but is not too wet. Squeeze together with your fingertips to make a homogenous dough. Shape into two discs and wrap in plastic wrap. Rest in the fridge for at least two hours, or preferably overnight.

FILLING AND ASSEMBLY

1. On a lightly floured surface, roll one disc into a circle slightly larger than your pie dish. You want it to be approximately ⅛ inch (3mm) in thickness. Line a 9" pie dish, leaving the extra dough overhanging. Trim the dough so there is about 1 inch overlapping the edge of your dish. Place in the fridge while you prepare the filling and lattice.
2. Roll out the second disc of dough into a rough rectangle approximately ⅛ inch thick. Use a pastry cutter to cut strips approximately 1 inch wide - these will be used for your lattice.
3. In a large bowl, toss together the peach segments, blueberries, sugar, arrowroot, vanilla paste, and salt. Taste and adjust the sugar if necessary, depending on the sweetness of your fruit. If the filling seems especially wet, adjust the amount of arrowroot. Transfer the filling to the pie dish, leaving any excess liquid behind.
4. Arrange the strips of pie dough on the top of the pie, weaving a simple lattice. Trim any overlapping pie dough and lattice strips so that they are flush with the edge of the pie dish. Carefully roll the edge of the pie dough back on itself slightly slightly, and crimp with your fingers.
5. Rest the pie in the fridge for at least 30 minutes. While the pie is resting in the fridge, preheat the oven to 425˚f/ 220˚c. Place a baking tray on the bottom rack of the oven. 
6. Brush the pie with egg wash, and sprinkle liberally with raw sugar. Bake at 425˚f / 220˚c for 20 minutes, or until the pastry is set and beginning to go golden. Reduce the temperature 375˚f / 190˚c, and bake until the pastry is deeply golden and the filling is bubbling. 
7. Remove from the oven and cool on a wire rack. Serve warm or at room temperature.