1To make the crust:
In a medium bowl, whisk together flour, sugar, and salt. Add cold, cubed butter and using your fingers, work the butter into the flour mixture. Quickly break the butter down into the flour mixture, some pieces will be the size of oat flakes, some the size of peas. Stir together the ice water and vinegar. Create a well in the butter and flour mixture and pour in the water/vinegar mixture. Use a fork to bring the dough together (I did this in a circular motion, turning the bowl). Try to moisten all of the flour bits. On a lightly floured work surface, dump out the dough mixture. It will be moist and shaggy, that's perfect. Divide the dough in two and gently knead into two disks. Wrap each disk in plastic wrap and refrigerate for one hour.
2To make the filling:
Wash and slice the peaches. In a medium bowl, combine peach slices and blueberries. In a small bowl, whisk together sugar, spices, flour and cornstarch. Pour the sugar mixture over the fruit and gently toss together with a wooden spoon (the fruit is going to get a bit smashed, that's fine!). Stir in the lemon juice. Place bowl of fruit in the fridge to rest while you roll the crust out.
3Preheat the oven to 400 degrees F. Place a rack in the center of the oven and place a baking sheet on the lower rack, just below where your pie will be. This will keep your oven clean from bubbling pie juice!
Remove one of the pie dough disks from the fridge. On a lightly floured surface, roll dough out into about a 13-inch round. Roll the dough a few strokes, then use your fingers to move it around the floured surface. This will ensure that the dough isn't sticking. When you roll the dough and you can see it start springing back, that means the butter is warming and you should stop rolling. Gently lift the round from the floured surface and place it into your 9 inch pie dish. Place back into the fridge while you roll out the other half. Roll out the second half, same as the first. Remove the bottom crust and fruit from the fridge. Gently pour the fruit filling into the pie dish. Carefully remove the top crust from work surface and drape over the fruit in the pie dish. With a small knife, trim the crust, leaving 3/4 inch overhang. With your fingers, press the top and bottom crusts together and fold under. Use a fork or your fingers to crimp the edges of the dough. Cut five small slits in the top of the crust so the juice and steam can vent. Brush lightly with beaten egg and sprinkle with cinnamon and sugar mix.
4Place pie in the oven and bake at 400 degrees F for 15 minutes. Reduce the oven heat to 375 and bake for 45-55 more minutes. Remove from the oven when crust is browned and the juices are bubbling. Remove from oven and allow to cool 2 hours before serving. Place covered in the fridge to store. Lasts 3-4 days (if it's not eaten by then!).