How to Make It
Light a grill or preheat a grill pan. Trim the ends off the lime and slice the lime crosswise 1/4 inch thick. Dust both sides of the lime wheels with sugar and grill over high heat, turning once, until lightly caramelized, about 20 seconds per side.
In a rocks glass, muddle the lime wheels with the 2 tablespoons of sugar. Fill the glass with ice, add the cachaça and soda, if using, and stir well.