To prepare crust, whisk ice water and sour cream together in a bowl.
Process flour and salt in food processor until combined. Scatter chilled butter over top and pulse until butter is size of small lentils.
Drizzle half of the sour cream mixture over top and pulse until incorporated, about 3 pulses; repeat with remaining sour cream mixture.
Pinch dough with your fingers; if dough feels dry and does not hold together, add 1 or 2 tablespoons more ice water and pulse until dough forms large clumps and no dry flour remains, 3 to 5 pulses.
Divide dough into 2 even pieces. Form each dough into 4-inch disk, wrap tightly in plastic wrap, and refrigerate for 1 hour.
Before rolling dough out, let it sit on counter to soften slightly, about 10 minutes.
Roll 1 piece dough into 12-inch circle on lightly floured counter. Loosely roll dough around rolling pin and gently unroll it onto 9-inch pie plate, letting excess dough hang over edge. Ease dough into plate by gently lifting edge of dough with your hand while pressing into plate bottom with your other hand. Wrap loosely in plastic wrap and refrigerate until dough is firm, about 30 minutes.
Roll second piece of dough into 12-inch circle on lightly floured counter, transfer to parchment paper-lined baking sheet and cover with plastic, refrigerate for 30 minutes.
To prepare pie filling, toss peaches and blueberries in a medium bowl. Mix the remaining filling ingredients and pour it over the fruit, gently toss together with a wooden spoon. Let sit at room temperature for 30 minutes.
Preheat oven to 425F. Pour the pie filling into the prepared bottom pie shell. Drape the top crust over the filling. Crimp dough evenly around edge of plate using your fingers.
Mix the egg wash ingredients, and brush the dough with the mixture.
Set pie on a large cookie sheet. Bake about 25 minutes, until the crust is light golden brown. Reduce oven temperature to 375F, and continue baking for another 25 minutes, until filling is bubbling and the crust is deep golden brown.
Remove pie from oven, and let it sit in room temperature for 30 minutes. Serve with vanilla ice cream.