Preheat the oven to 350 degrees.
Roll half of your pie dough for the bottom of the pie. Make sure to roll large enough to get a 1-2 inch overhang all the way around. Place in the fridge while you prep the filling.
Mix nectarine wedges, blackberries, sugar, and cornstarch in a bowl. I use a rubber spatula, so I don't break up the fruit. Pour into prepared pan.
Next, decide on how you want to cover the top. If you have a solid top, make sure and cut some vent holes. If not, you can do lattice as I did.
Fold under your overlap on the bottom crust. Crimp how you choose.
Mix your egg and milk in a bowl and lightly brush over the top. Sprinkle with sugar.
Bake until golden brown and the fruit is soft, but now mushy. If your top crust is getting too dark, cover lightly with a piece of tinfoil.
Remove from oven. You can either serve it immediately or wait until it has cooled. It is easier to cut cool, but if you like it warm, I say go for it!
It is delicious served on its own, with ice cream, whip cream, or even pastry cream. The sky is the limit here!