Recipe makes about 1½ cups simple syrup, enough for 14–16 drinks; mojito recipe is for each cocktail
Measure sugar and water into a saucepan and bring to a light boil. Reduce heat and simmer until sugar is dissolved then add the mint leaves, crushing and tearing them with your fingers as you add them to the syrup. Simmer one minute and then cover, remove from heat, and allow to steep for 30 minutes.
Strain into a jar and discard the mint leaves. Cool to room temperature and keep refrigerated. Lasts a long time.
With a muddler, crush a few mint leaves in the bottom of a chilled highball glass. Pour in lime juice, simple syrup, and rum. Fill glass with crushed ice and stir. Add sparkling water to taste. Garnish with lime wedge and optional mint sprig.