1. Preheat the oven to 325°F
2. In a small bowl, beat together egg, water and salt to make egg wash and set aside.
3.In a bowl, mix together flour, sugar and salt.
4. In a large bowl, put the blackberry puree and whisk in the flour mixture, until well mixed.
5. In the pie crust, place the whole blackberries and pour the black berry puree and leave it aside.
6. On a clean working table, dust flour and roll pie dough about 10 inches round.
7. Using a paring knife, make 4 large and 4 small slits in the center of rolled dough.
8. Wrap the rolled dough over the rolling pin.
9. Brush the edges of piecrust with egg wash.
10. Carefully place the rolled dough over filled piecrust and cut the extra dough off the edge.
11. Using a fork, press the edges of the pie to seal.
12. Apply the egg wash on the top, using brush.
13. Sprinkle 1 teaspoon of sugar on top.
14. Bake the pie in the oven for 35 to 40 minutes or until the top gets golden brown color.
15. Remove the pie and allow to cool at room temperature for 2 hours.