Preheat the oven to 160 °C.
Sift the flour and half the sugar together a few times to incorporate as much air as possible.
In a separate bowl whisk the egg whites until foaming.
Add the cream of tartar and salt and continue beating until the egg whites are stiff but not dry.
Add 25 ml of the remaining sugar to the egg whites and beat well.
Add the remaining sugar 25 ml at a time, beating well after each addition.
Sift a thin layer of the flour mixture over the egg whites and fold in.
Proceed as described until all the flour mixture has been folded in.
Fold in the almond or vanilla essence.
Carefully turn the batter into an ungreased 24 cm angel cake tin and bake for one hour.
Invert the pan on a wire rack and leave the cake to cool in the tin.
Loosen the sides of the cake and remove from the pan.
610 kJ a serving ? this deliciously light cake is low in cholesterol and fat.
Variation: To make a chocolate sponge cake, sift 80 ml sifted cocoa powder and 10 ml sifted instant coffee powder along with the flour.
Continue as described.