Warm a 5–6 ounce ceramic cup with hot water, then dry it. Purge the espresso machine group head and steam wand.
Grind 0.25 ounces finely ground coffee beans for a single shot; dose and level into the portafilter, then tamp firmly and evenly.
Lock in and pull a 1-ounce espresso shot, 25–30 seconds total, stopping as the stream blonds to a pale honey color.
While the shot pulls, steam 4 ounces whole milk: stretch gently until about 100°F (a soft paper-tearing sound), then submerge the tip to texture to 140–150°F, 20–40 seconds total, until glossy and free of large bubbles. Tap and swirl the pitcher to polish a fine microfoam.
Immediately pour the milk into the espresso: start higher to integrate, then lower and increase flow to finish with a velvety foam cap about 1–2 cm thick. Serve at once.
Add granulated sugar to taste (for serving), if desired.