Preheat the oven to 300 degrees F (150 degrees C).
In a large bowl, sift together the Almond Flour (40 gram), Powdered Confectioners Sugar (40 gram), and Matcha Powder (1 tablespoon).
Beat the white of an Egg (1) on low speed using an electric mixer until it is white and frothy, approximately 1 minute.
Gradually add the Caster Sugar (45 gram) 1/4 at a time. When the first addition of sugar has completely dissolved, increase the mixer speed to medium and add until all the sugar has been incorporated. Continue to beat until stiff peaks form.
Add the meringue to the sifted ground almond flour and icing sugar. Using a spatula, start the macaronage process until you get a molten-like mixture that drips down like a ribbon when lifted. Add a bit of Green Food Coloring (to taste) to get a greener Christmas wreath.
Transfer the batter to a piping bag with a round tip and pipe out macarons. Pipe a Christmas wreath by drawing the outline of a circle. Do not pipe lines that are too thick, as the batter will spread and you want to retain the hole.
After piping, knock the bottom of the tray against a flat surface to get rid of air bubbles. Let the shells dry for approximately 30 minutes, or more, in an air-conditioned room. You should be able to touch them gently with the tip of your finger without them sticking.
Bake wreaths in a preheated oven at 300 degrees F (150 degrees C) for approximately 10-13 minutes. Let them cool.
Place Caster Sugar (50 gram) and the white of the Egg (1) in a metal bowl over a saucepan of simmering water. Whisk continuously until the sugar is dissolved. It is natural for the egg mixture to become thick and sticky.
Beat the egg white mixture using an electric mixer with a whip attachment on medium-high speed until stiff peaks form.
Continue beating at medium-high speed while adding small chunks of Unsalted Butter (75 gram) gradually. It might curdle, but keep beating until the butter is blended in and the buttercream is smooth.
Sift in Matcha Powder (1 tablespoon) and mix well. Chill slightly before using.
Pipe frosting between 2 macaron shells and decorate with Royal Icing (to taste). Serve and enjoy!