Use ceremonial-grade matcha only — culinary grade turns bitter and chalky when frozen. Sift it and make the paste first; matcha clumps will not break up during spinning. Keep whisky at 1 ½ tsp for proper freezing. Japanese whisky has a very fine line between freeze point and slush. Ask me how I know (three fails before I got it correct). The finished ice cream should be a vivid, even green — any streaks mean the paste wasn’t fully incorporated.