Pull two shots of espresso (about 2 ounces) using a warmed espresso machine (around 90°C water temperature), extracting for 20–30 seconds.

Fill a tall glass (10 to 12 ounces) about three-quarters full with ice cubes.

Carefully pour the hot espresso over the ice in the glass.

Slowly pour 4 to 5 ounces of chilled tonic water into the glass, maintaining a 1:2 ratio of espresso to tonic.

Use a long bar spoon to stir gently 3–5 times, mixing the espresso and tonic without losing carbonation.

Squeeze one fresh lemon or lime wedge directly over the drink to express oils and juice.

Drop the squeezed citrus wedge into the glass as a garnish.

Taste the drink and adjust balance: add more tonic if too strong or another espresso shot next time if too light.