Mix flour, sugar, salt in a bowl. Cut in cold butter. Break up butter and slowly add cold water. Divide into two discs, wrap in plastic wrap, and place in fridge for 30 minutes.
Blackberry Filling
Combine all the ingredients for the blackberry filling in a medium saucepan. Stir and turn the heat up to medium-high.
As the berries cook, squish them with a potato masher. Stir and allow the mixture to come to a simmer. Once thickened, remove from the heat.
Cheesecake
In a medium-sized mixing bowl, combine all the ingredients for the cheesecake. Make sure they are all at room temperature so they mix easily. With an electric hand mixer, whisk the ingredients until smooth.
Assemble
Preheat the oven to 400 degrees
Roll one disc of pie dough out and press it into a greased pie dish
Pour the cheesecake filling and then the blackberry filling on top of the cheesecake batter.
Roll the second dough disc out and place it on top of the pie. Pinch and design the outer edge of the crust.
Cut a ventilation hole in the center of the pie, I typically do an X.
Take the egg white and milk, whisk them together, then brush the pie with the egg wash using a pastry brush.
Place the pie in the oven and bake for 30 minutes
Place a piece of tinfoil on top of the pie and turn the oven down to 375. Bake for an additional 30 minutes
Remove from the oven and allow it to cool for about an hour.
Cover and place the pie in the fridge for at least 4 hours to chill before serving.