Butter a 1.2-litre pudding basin. Sift the flour, baking powder and a pinch of salt into a large bowl and, using your fingertips, rub in the butter. Stir in the suet, sugar, lemon zest and currants. Stir in the egg and add enough milk to mix to a soft consistency.
Spoon into the basin. Cover with buttered kitchen foil, making a pleat across the centre, and tie with string.
Steam for 2 hours or until well risen and firm. If you don’t have a steamer, place the pudding in a large saucepan on an upturned saucer. Pour boiling water to halfway up the basin, then cover and steam for 2 hours. Check the water level every now and then, and top up if you need to. To serve, turn out onto a warm plate and pour over the golden syrup.