Ice cream or sweetened whipped creamto serve, optional, but suggested
Preheat the oven to 400 F.
In a large bowl, combine the flour, sugar, salt, and lemon zest. Add the blueberries and peaches, and toss to combine. Sprinkle over the lemon juice, and toss again.
Roll the pastry crust onto a greased cookie sheet. Heap the fruit mixture into the middle, leaving about an inch of dough as a border, then fold up the dough around the edges up over the fruit (the middle will have a lot of fruit showing). Dot the fruit with the butter, and brush the dough around the edges with the beaten egg. Sprinkle the egg-brushed dough with a bit of granulated sugar.
Bake for 30 to 40 minutes, until the fruit is bubbly, and the crust is firm and browned. Cool slightly or completely on the pan.