In a medium sized non-stick frypan, saute onion on a medium heat until tender and slightly brown. Add meat curry powder and cook for a further 10-20 seconds. Add chicken and stir fry until cooked, then remaining ingredients and stir-fry until potatoes are tender. Taste and add more salt and/or sugar if required. Cool slightly before covering with cling wrap and refrigerating.
To make shortcrust pastry, combine flour, salt and butter in a large mixing bowl. With your fingers, rub butter into flour vigorously until you achieve a crumbly consistency. Add very small amounts of water at a time to bind the mixture into a firm, single mass. Roughly shape into 3 disks, cover with clingwrap and rest in fridge for 20 minutes.
Alternatively, combine all ingredients except water in a food processor. Pulse until the mixture is a crumbly consistency, then add very small amounts of water at a time (by the tablespoon), pulsing until the mixture forms a single mass. Roughly shape into 3 disks, cover with clingwrap and rest in fridge for 20 minutes.
To stuff curry puffs, dust bench with flour and roll pastry until 3mm thick. Cut 10cm circles with a pastry cutter, fill with a tablespoon full of mixture and crimp edges to seal. Repeat until all pastry or filling is used up.
Heat oil in a large pot or wok. Drop a very small portion of pastry into oil. If it turns golden in about 15 seconds, the oil is ready. Fry 4-5 pieces of curry puff at a time until the pastry is beautifully golden.