Dissolve the matcha. Use a fine-mesh strainer to sift the matcha into a heatproof measuring cup or small bowl (preferably one with a spout). Add the sugar and pour the hot water over mixture. Use a bamboo whisk to vigorously whisk the mixture in the shape of a "W" for about 30-45 seconds until no clumps remain and the mixture is slightly foamy.
Combine. Pour the matcha mixture into a mug, then top with the steamed milk.