Cut the cold butter into 1/2" cubes and divide into two parts: 9 TBS and 5 TBS.
Wrap each part with plastic wrap. Place the large amount in the refrigerator and the smaller part in the freezer for a minimum of 30 minutes.
Sift together the flour, baking powder, and salt. If time permits, place the mix in a plastic bag and freeze for about 30 minutes.
Place the flour mix in a bowl of a food processor and pulse about 3 times.
Add the large part of the butter and process for about 10 seconds, until the mixture resembles a coarse meal.
Add the smaller part of the butter and process until the butter is the size of large peas. About 10 seconds.
Add the water and vinegar and process until the butter is the size of small peas. About 5-10 seconds.
The mixture should look grainy and will only hold together when pinched with your fingers.
Place the mixture on a clean surface and using the palm of your hand press it all together to form a disk.
Divide the dough into two, one part slightly larger than the other (2/3-1/3). Wrap each part with plastic wrap and refrigerate for a minimum of 1-hour or overnight.
About an hour before baking time, remove the dough from the refrigerator and roll it into 1/8" thick 12" circle. Gently lift the dough and place it in a 9" x 2" pie pan. Shape the top tedges using the knuckle of your finger. Place back in the refrigerator for about 30 minutes.
Roll the smaller part of the dough into 10"-12" circle and use a leaf-shaped cookie cutter to create the design. Place the rolled dough on a cookie sheet lined with baking paper and return to the refrigerator to cool.
About 30 minutes before baking, preheat oven to 400F. Place an oven rack at the lowest shelf and line a large baking pan with baking paper.
Place the filling ingredients in a large bowl and gently toss for even distribution.
Remove the pie shell from the refrigerator and pour the blackberry filling in.
Place the top crust on top of the filling and seal the edges.
Brush the pie with the beaten egg. Sprinkle with turbinado sugar.
Bake on top of the line baking pan for 50-60 minutes or just until the filling in bubbling.