Place watermelon and honey into the blender. Add the juice of both limes, but be sure to zest the juice first, if preparing the mint lime sugar. Blend until well combined. Give the mixture a quick taste test to see if additional sweetener needs to be added.
Using a fine mesh strainer, strain the watermelon mixture over a 9x9 freezer safe container.
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.
Scoop out granita into serving dish and sprinkle with a teaspoon of Mint Lime Sugar.
Granita will stay in the beautiful icy consistency in the freezer in an airtight container for up to 2 months.