Pre-heat oven to 200°C. Line a large biscuit tray with baking paper.
Place Fate Mix, custard powder, sugar, and margarine in a mixing bowl. Using a large spoon, mix well until a dough is formed. Rest, 5mins.
Place dough on a clean work surface dusted with extra Fate Mix. Using a rolling pin, roll dough to form a 20cm x 20cm square.
Slice square into 2 even pieces, then slice each half into 5 equal sized fingers, which are horizontal to each other, and at right angles to the initial cut. Using a fork, prick shortbread.
Slice square into 2 even pieces, then slice each half into 5 equal sized fingers, which are horizontal to each other, and at right angles to the initial cut. Using a fork, prick shortbread.
Place biscuits on the tray, bake 15mins., or until just golden.
Remove from oven, allow to cool on a wire rack. Sprinkle with extra sugar if desire