To make the filling: Heat a little oil in pan and fry onion until soft. Add chicken, curry powder, chilli powder and tumeric and stir-fry until chicken is cooked. Add the potatoes, season with sugar, salt and pepper and cook for another 5 minutes. Mix well then remove from heat and set aside to cool.
To make the pastry: Make a well in the center of the flour and add the butter cubes a little at a time, mixing it with the flour and adding a bit of water at a time. Season with a little salt. Knead the mixture well and let it rest in a cool place for 30 minutes.
Roll the pastry dough out on flat surface and cut into 8 cm diameters. Take a tablespoon of the filling and place in the center of dough. Fold pastry over and crimp the edges together.
Heat oil in wok until hot and deep fry the pastry until golden brown. Drain on paper towel and serve.