4 cups of cubed, seedless watermelon
1/2 cup sugar
Juice from one lime
1 tablespoon of freshly grated ginger root (optional)
In the bowl of a food processor (or a blender), pulse watermelon, sugar and lime juice until smooth. If using, place grated ginger in a paper towel and squeeze juice into the puree. Pulse again to blend.
Place a fine-mesh strainer over a large bowl and pour watermelon mixture through it, pressing on the solids to extract every last bit of juice into the bowl. Discard (or eat solids) and pour the juice into a 9x13 inch pan, and place in the freezer.
After one hour scrape mixture with a fork. Repeat hourly for the next three hours which will give the granita a fluffy, granular texture. Spoon into small bowls and serve.