Prepare a baking sheet with parchment paper or a silicone mat.
Sift the almond flour on a scale until you reach 105 grams, removing any larger pieces. Repeat with the powdered sugar, then add the matcha powder. Mix the almond flour, powdered sugar, and matcha together until thoroughly blended, then set aside.
Place the egg whites, granulated sugar, and egg white powder into the bowl of your stand mixer and whisk together. Set the bowl over simmering water, making sure it forms a tight seal and the bottom doesn't touch the water.
Whisk continuously while heating the mixture to 60°C. Once it reaches temperature, remove from the heat and transfer to your stand mixer fitted with the whisk attachment.
Whip on low speed, increase to medium once soft peaks form, then to high until stiff peaks form. If using food coloring, add it now and whip just until incorporated.
Sift the dry ingredients over the meringue and gently fold them in, being careful not to overmix. The batter is ready when it flows off the spatula in a ribbon, without stopping, but not too quickly.
Transfer the batter to a piping bag fitted with a medium or large round tip, then pipe small 3 to 4 cm circles onto a parchment lined baking sheet.
Tap the baking sheet firmly against the counter several times to release air bubbles, popping any remaining ones with a toothpick.
Preheat the oven to 150°C (135°C for convection). Let the macarons sit until a skin forms on top, 8 minutes to an hour, until they can be gently touched without sticking.
Bake for 15 to 20 minutes, checking after 15 minutes and every minute after, until the tops are firm and the bottoms don't move.
Let the macarons cool completely, then match the shells into pairs and set aside for filling.
Place the chopped white chocolate in a heatproof bowl. Bring the cream and matcha powder to a boil, pour over the chocolate, and let sit 2 minutes before stirring smooth. Cover and cool to room temperature before using.
Pipe the matcha white chocolate onto half of the macaron shells, sandwich with the remaining shells, and refrigerate overnight before serving.
