3 egg whites (at room temperature, use 3-4 days old eggs)
Beat egg whites until foamy, then add in cream of tartar and beat at high speed until soft peaks form. Add in sweetener gradually (spoon by spoon) while beating, then continue to beat at high speed until VERY stiff. Add in green tea powder gradually and mix until combined. Fill the green tea meringue into a piping bag with your favourite tip, then pipe dollops onto silicon mats (or cookie sheets lined with parchment paper). Bake in the preheated oven for 1 hour 10 minutes. Let the meringue cookies cool in the closed oven for 1 hour. Transfer with care (the cookies are fragile) to airtight containers immediately.