BASIC RULE: You will always need twice the amount of sugar relative to the egg whites. So in this case I am using 70g egg whites, so I need 140g sugar.
Preheat oven to 200 C. Spread the sugar on a tray and bake for 5 minutes.
Meanwhile whisk the egg whites until they form stiff peaks. When done, add the warm sugar spoon by spoon. Keep whisking for about 5 minutes until you can feel no more sugar grains between your fingers.
Add flavouring and colour of your choice.
Fill your piping bag. Put it in a glass to stabilise it. Cut off the tip and start piping. It helps to pipe a bit of the mixture underneath the edges of the baking paper to prevent it from moving.