In a mixing bowl, combine the plain flour, salt, and optional ground turmeric. Cut in the very cold frozen butter and vegetable shortening until the mixture resembles coarse crumbs, about 5 minutes. Gradually add icy cold water until a dough forms. Shape into a disc, wrap in plastic, and chill in the refrigerator for 30 minutes.

Heat a skillet over medium heat and add the minced beef, cooking until browned, about 5-7 minutes. Stir in finely chopped onions and minced garlic, cooking for an additional 3 minutes until the onions are translucent. Season with thyme, black pepper, and Jamaican curry powder, stirring. Pour in the beef stock and soy sauce, letting it simmer until thickened, approximately 8-10 minutes. Remove from heat, mix in breadcrumbs, and allow the filling to cool.

Preheat your oven to 190°C (375°F). On a floured surface, roll out the chilled dough to about 3 mm thick. Use a round cutter to cut out circles. Place about one tablespoon of the cooled beef filling on one half of each circle, fold the dough over, and seal the edges with a fork.

Line a baking tray with parchment paper and arrange the patties on it, leaving space between. Beat an egg and brush the tops of the patties. Bake in the preheated oven for 20-25 minutes, or until golden brown and flaky.