Begin by putting 3 egg whites in a bowl, if you no longer remember how many you have, weigh: an egg-white weighs about 30 grammes. Then weigh 150 gcaster sugar (50 grammes per egg-white needed), to use later for making meringues.
Continue beating until egg whites are firm. A very old knack to know if egg white are beaten sufficiently: you can put a whole egg onto them and it will stay on the surface. Another old saying: " egg whites are never beaten enough ".
And while still beating, incorporate the remaining sugar tablespoon by tablespoon.
You will get a very bright white mixture.
Put mixture in small heaps on a non-stick baking sheet (with 2 tablespoons for example). Then put in the oven at 100░C or 212░F for 4 - 6 hours or better, overnight. If you cook in a wood-fired oven, cook overnight. Note: You can decorate meringues before baking by sprinkling them with flaked almonds, and/or with a pinch of cocoa powder.
After cooking, place on a rack to cool. Keep in an airtight tin.