Preheat your oven to a very low temperature of about 60C/140F. You can use a higher temperature if you wish however a low temperature helpt to stop cracking

Separate your egg whites from the yolk. Make absolutely certain that there is no yolk at all in your mixture

Weigh out your sugar

Whisk up your egg whites on a low-speed setting until they are frothy

Now, still using a low-speed setting, very slowly add your sugar and whisk as you add each spoonful

Increase your speed to medium and keep whisking until your mixture reaches a firm peak (see the article below for details) Note You may need to reduce the speed back down again towards the end when the mixture is thicker.