Preheat oven to 110 deg C.
Beat egg whites until it starts to stiffen.
Beat in the castor sugar, one tablespoon at a time, until all castor sugar is incorporated and the egg whites are really stiff.
Sift a third of the icing sugar onto the egg whites and fold in gently.
Repeat twice more until all icing sugar is incorporated.
Spoon tablespoon of mixture onto baking trays lined with baking paper.
Bake for about 1hr 15 mins, turn oven off, open the door, and allow to cool.
To make chocolate meringues, replace a couple of spoons of icing sugar with the same amount of cocoa, and proceed as above.
Fold 4 blocks of dark chocolate, chopped finely, into the mixture before spooning out.
For coffee meringues, replace 2 teaspoons of icing sugar with the same amount of instant coffee. Be sure to sift very well.
Proceed as above.