Add 2 bar spoons of mint-infused sugar to a frozen highball glass.
Rinse a fresh handful of mint and add it to the glass.
Quarter ½ a lime and place it peel side down into the glass.
Muddle gently to release lime juice and mint oils—avoid shredding the mint.
Add simple syrup, lime juice and light rum. Stir to combine.
Taste and adjust sweetness or acidity if needed.
Fill the glass ¾ full with crushed ice and churn with a spoon to mix.
Top with a splash of sparkling water and more crushed ice to fill.
Garnish with a fresh mint bouquet (give it a quick slap) next to a straw and serve