Combine the cherries, balsamic vinegar, and sugar in a small saucepan over medium heat.

Bring to a gentle simmer and cook for 10 minutes, mashing the cherries with a spoon as they soften, until the liquid turns deep burgundy and coats the spoon.

Remove from the heat and cool completely, about 30 minutes.

Strain through a fine-mesh strainer into a jar, pressing on the cherries to extract every drop; the shrub keeps refrigerated for three weeks.

Fill a coupe glass with ice, or skip the ice and chill the glass in the freezer for 10 minutes beforehand.

Pour 1.5 ounces of the cherry balsamic shrub into the glass.

Top with the chilled soda water and stir once, gently.

Garnish with two cherries on a pick, resting across the rim.