Egg white 100
Milk powder 130
Green tea powder 30
Place 1) into a small pot, making sure sugar does not come into direct contact with sides of pot. Heat over small flame until melted, then bring to a vigorous bubble until it reaches 120C. This will take at least 20 minutes. In the meantime, combine 4) and sieve. Melt butter for easier incorporation. When sugar syrup is almost at 120C, whip whites and sugar until firm peak. While whipping. Pour syrup into whites in a thin stream, avoiding the beater and sides of the bowl. Beat until peaks are firm and glossy. Add butter, beat to incorporate. Add dries, beat to incorporate.
At this point, can allow it to cool for a bit before scraping directly into a piping bag or a bowl. Keep at room temperature for a couple days or in the chiller, where it will firm up.
Update: not suitable as macaron filling as it’s too firm from the chiller and melts fast.