Sift the almond flour, matcha powder and icing sugar together into a bowl.
In another bowl, whisk the egg whites to stiff peaks, adding the granulated sugar in three additions.
Add the dry ingredients to the whipped egg whites.
Fold with a spatula and start the macaronage. The batter should be smooth and fall in a ribbon.My own tip: press the batter against the side of the bowl with the spatula while turning the bowl. Scrape it back together, then start again.A successful macaronage is what gives you a lovely foot around the shell as it bakes. Transfer the batter to a piping bag fitted with a plain round tip.
Line a baking tray that fits your oven with a sheet of baking paper.
Pipe the batter onto the paper in rounds 2cm across. No bigger, because the batter spreads on its own and the shells would end up too large.
Once everything is piped, pick up the tray and tap it gently against the worktop.This bursts any bubbles sitting on the surface of the shells and spreads them out to about 3.5cm across. Leave the shells to dry for 1 hour. The tops should no longer feel tacky. A fan at a sensible distance will speed things up.
Bake at 150°C for 20 minutes. The shells should lift off easily.