Pit the salted plums if whole and roughly chop the flesh. Combine the chopped salted plums, sugar, water, and lemon zest in a small saucepan over medium heat.

Bring to a gentle simmer, mashing the plums with the back of a spoon to release juice. Simmer for 6–8 minutes until the mixture becomes syrupy and the sugar is fully dissolved.

Remove from heat and let cool slightly. Strain the mixture through a fine mesh sieve into a jar, pressing on solids to extract as much liquid as possible. Discard (or reserve) solids. Chill the syrup until cold. This yields roughly 60–70 ml of concentrated syrup; use 30 ml per serving.

Black Tea Concentrate

Brew a strong batch of black tea by steeping 2 tsp loose tea (or 2 tea bags) in 120 ml near-boiling water for 5 minutes to create a concentrated brew. Strain and cool to room temperature, then chill in the refrigerator until cold. Use 60 ml per serving.

Cocktail Assembly

If you like a salty rim, rub a lemon wedge around the glass rim and dip lightly in coarse sea salt; otherwise omit.

Fill a highball or Collins glass with ice.

Add 30 ml plum-shiso syrup, 15 ml fresh lemon juice, and 60 ml cold black tea concentrate into the glass.

Stir gently to combine the syrup, lemon and tea.

Top with 120 ml chilled club soda to taste, giving a gentle stir to integrate without flattening the soda.

Garnish with a lemon wheel or a thin slice of plum. Optionally, sprinkle a tiny pinch of coarse sea salt on top to accentuate the salted-plum character.

Serve immediately with a straw or stirrer.