Pulse pistachio in a food processor until coarsely ground.
Add flour, salt, sugar, flax seeds and add cold butter just until coarse meal forms, then gradually add 1/2 cup iced water until the dough comes together.
Form into a ball and wrap in plastic. Chill at least 30 minutes.
Preheat oven to 400F.
Mix all of the filling ingredients together and add to the centre of the dough leaving 2.5 inches of empty crust for the fold.
Fold the dough around the filling and slightly brush the folds with flax + water ( egg replacer ) and cover with flax seeds.
Cook for about 40 minutes or until brown.