I have opted to give you a master recipe here for vanilla french macarons instead of my flavor variations. See the notes for instructions on how to infuse the cream with tea leaves to flavor the buttercream.
In the bowl of a stand mixer fitted with the whisk attachment, beat the egg whites until frothy. Add sugar and beat until stiff and glossy (stiff peaks). Add the extract and mix until fully incorporated.
To infuse the cream for a tea-infused buttercream, heat the cream over low heat in a small saucepan with one tea bag or a tablespoon of tea leaves (strain the cream before adding it to the buttercream). You may need to add more powdered sugar to bring it back to the right consistency after adding the cream.