Tip your egg whites into the bowl of a free standing mixer and whisk on a low speed, getting faster as you build up a foam. Alternatively you can do this with an electric hand whisk.
Once the egg whites form firm peaks, start adding your caster sugar a little at a time, with the mixer still running. It is important to wait until this stage, or the meringue can turn runny. As a rule, use 55g caster sugar per egg white. When ready, the meringue should be glossy and thick like shaving foam.
Spoon onto a baking sheet lines with non-stick parchment in whichever shape you prefer. Bake at 140C/120C fan/gas 1 for 1 hour 15 minutes until the meringues have a crisp shell and easily peel away from the paper.
Turn the meringues into a simple dessert by sandwiching them together with sweetened whipped cream.