Place half the watermelon, half the lime juice and half the sugar in a blender (or a tall bowl suign a stick blender) and process until smooth. Pour into a 9x13 baking dish. Process the other half of the watermelon, lime juice and sugar until smooth and add to the baking dish.

Transfer dish to the freezer, making sure it is stable and level. Freeze for 2-3 hours and then begin the process of scraping the top frozen layer. Taking a fork, lightly scrape the top layer of your juice until you have fine crystals. Return the pan to the freezer with the shaved ice on top.

Remove a couple hours later and continue scraping. Repeat this scraping process every couple hours until everything is shaved. Store, covered in plastic wrap, in the freezer until serving. Serve in a pretty glass with a twist of lime or a basil leaf.