Freeze the watermelon juice for two or three hours, then begin the process of lightly scraping the top frozen layer with a fork. Return pan to freezer with the shaved ice on top; remove a couple of hours later and continue scraping. Repeat the occasional scraping process until the entire mixture is shaved.
Mint Lime Sugar
Mince the lime zest and mint leaves very finely. Toss with the sugar and a dash of salt.
To serve: Scoop out granita into serving dish and sprinkle with a teaspoon of Mint Lime Sugar.
Be sure to use maple syrup and omit serving with mint lime sugar to keep these granitas a paleo snack. By using maple syrup in place of honey, this also becomes a vegan dessert.