Method

• 1.
  Place lime, sugar and three-quarters mint in a large bowl or jug and muddle with the end of a rolling pin. Stir through rum and stand for 1-2 hours to infuse. Strain mixture through a sieve set over a bowl, pressing with the back of a spoon to extract juice.
• 2.
  Remove rind from 1 watermelon half and coarsely chop flesh. Spread on a freezer-proof tray and pour over half rum mixture. Cover with plastic wrap and freeze for 6 hours or until frozen. Cut remaining watermelon half into wedges, place on a tray and drizzle with remaining rum mixture. Chill until needed.
• 3.
  Place frozen watermelon mixture in a food processor and pulse, stirring occasionally, until a snowy consistency.
• 4.
  Transfer to a platter. Working quickly, top with watermelon wedges, extra zest and remaining mint leaves. Serve immediately.