Whip egg whites for 5 minutes at medium speed. Then gradually add half the caster sugar (75g /2.65 oz) ) while continuing to whisk.
Whisk for 3 minutes after incorporating this first portion, then gradually add the remaining sugar.
Whip for a further 3 to 5 minutes until the meringue is firm. Add the powdered sugar a little at a time, lowering the speed of the stand mixer to prevent it from flying away.
Note: If you're worried about the meringue falling over in the stand mixer, you can gently fold in the powdered sugar with a skimmer or maryse, without overworking the mixture.
Scrape down the sides of the bowl to bring the powdered sugar down to the center. Whisk for another 1 minute. The result is a very firm meringue with a bird's beak.
Divide the meringue among several bowls if you wish to color it.
Add a small amount of gel food coloring of your choice, then mix gently until you achieve an even color.
Use the piping tips suited for the design you want to create. I used Wilton's 1M tip to form roses and a PF tip for petit fours.
Preheat oven to 100°C ( 212°F). For very white meringues, you can set it to 90°C (194°F).
Fill piping bags with meringue.
For a bicolor effect, draw stripes of gel food coloring inside the piping bag, then fill it with meringue.
Place a sheet of baking parchment on a baking tray, applying a small amount of meringue to make it stick.
Pipe roses, gently pressing to remove the tip, or create small rosettes or other shapes as desired.
Bake for 1 to 1.5 hours at 100°C (212°F), or 1.5 to 2.5 hours at 90°C (194°F). The aim is to dry the meringues, not bake them.
Open the oven slightly at least 3 times during baking to release steam and prevent the meringues from cracking.
Remove them from the oven once they are completely dry and easily come off the baking sheet.