01 - In a large bowl, whisk together the flour, salt, and turmeric. Add the cold cubed butter and shortening. Cut the fats into the flour using a pastry blender or your fingertips until the mixture resembles coarse crumbs. Gradually drizzle in the ice water, stirring gently until the dough just comes together. Divide the dough into two equal portions, shape each into a flat disk, wrap tightly in plastic wrap, and refrigerate for at least 30 minutes.
02 - Heat the vegetable oil in a large skillet over medium heat. Add the onion and garlic, sautéing until softened and fragrant, about 3 minutes. If using, stir in the minced Scotch bonnet pepper. Add the ground chicken and cook, breaking it apart with a wooden spoon, until no longer pink throughout.
03 - Stir in the diced potato, curry powder, allspice, dried thyme, black pepper, and salt. Cook for 2 minutes to toast the spices. Pour in the chicken broth, cover, and simmer for 8 to 10 minutes until the potatoes are tender and the liquid has been absorbed into a thick filling. Fold in the scallions and parsley, then remove from heat and let cool completely.
04 - Preheat the oven to 400°F. Line a baking sheet with parchment paper and set aside.
05 - On a lightly floured work surface, roll each chilled dough disk to approximately ⅛ inch thick. Cut out 6-inch circles using a bowl or round cutter as a template. Gather and re-roll scraps as needed to yield 8 total rounds.
06 - Place 2 to 3 tablespoons of the cooled chicken filling onto one half of each dough round. Fold the other half over the filling to form a half-moon shape. Press the edges together firmly and crimp with a fork to seal. Transfer each patty to the prepared baking sheet.
07 - Brush the tops of the patties evenly with the beaten egg wash. Bake for 25 to 30 minutes until the pastry is deep golden brown and flaky. Allow to cool for 5 minutes before serving.