1/3 cup hot water (ideally 175 degrees F.; you can achieve this by boiling water, pouring it into a small pitcher or cup, then pouring it into your matcha bowl)
1 ice cube
Set a fine mesh strainer over a small bowl. Add matcha and gently sift into bowl.
Pour hot water over (again, not boiling, which kills the flavor) and, using a matcha whisk, begin whisking briskly in an M pattern back and forth across the bowl until foamy (about 30 seconds). You can make this with cold water — some say that cold water brings out more of the umami flavor — but you won’t get as much froth. Your call!
Add ice cube to bowl. Using whisk, gently stir until the cube melts*.
* My less-delicate American method: At this point I pour the matcha into a jar, add 3 ice cubes, then seal and shake until really foamy. Sometimes the ice breaks up, making a semi-slushie. And, of course, you can use milk or nut milk in the place of water, though Mrs. Watanabe politely disapproves: “I wouldn’t do it personally, but I’m okay with people doing it.”