Line a baking sheet with greaseproof paper and preheat the oven to 150°C.
Whisk the egg white until is has stiff peaks.
Whisk in the sugar a few tablespoons at a time - do this fairly quickly as too much whisking will make the eggs go runny again.
Use a spoon or a piping bag to put the mixture on to the baking sheet.
Put the meringues in the oven and immediately turn it down to 140°C.
After half an hour turn the oven off. DO NOT open the door. Leave the meringues in the oven for several hours (overnight works well) and they'll crisp up nicely.