cream butter and sugar together until light and fluffy; add eggs until well-incorporated. alternate folding in the flour and adding the cold tea into the mixture. stir until smooth, adding enough powdered matcha to reach a jade-coloured batter, or whatever shade you prefer. be careful adding more than a few tablespoonfuls as it can get quite bitter the darker you go.
fill paper-lined muffin tins and bake in a 350°F preheated oven for 20 minutes.