I have long planned to work on the meringue recipe, especially after the numerous questions about the use of egg whites. Although it seems a pretty obvious recipe, there are some small details that matter for a perfect result.
You can replace the powdered sugar with plain sugar, but you'll have more work to do and you won't get the perfectly glossy meringue very quickly. Also, you may not get it right from the first time because of the temperature in the oven. You might need several tries until you see how the perfect meringue reconciles with your oven, at least this is what happened to me.
In conclusion, it's worth all the effort. They are the simplest sweets, with no fat nor flour, very airy, they just melt in your mouth. You can add any flavors, colors, hazelnuts or chopped walnuts.
This recipe uses three egg whites (about 100g) and you'll have an oven sheet full of meringues. It's better to prepare several batches if you want more, because the meringue already mixed must be put in the oven right away, later it will lose its texture.