Preparation / Directions:
Chill a rectangular metal baking pan (about 15-by-9-by-2-inches) in the freezer. In a blender or large-capacity food processor, combine the lemon juice, water, sugar and lemon zest. Puree until the sugar dissolves, about 1 minute. Pour the lemon mixture into the chilled baking pan and freeze until ice crystals form around the sides and bottom of the pan, about 30 minutes. Carefully rake the mixture with a fork to loosen the crystals. Gently stir with the fork until the frozen and unfrozen elements are evenly combined. Do not break the crystals too finely, but break up any large clumps that might have formed near the edges. Return to the freezer.
Repeat this process every 20 minutes until the granita is the uniform consistency of soft crushed ice. This will take about 2 hours in most freezers. Serve immediately or store in an airtight container in the freezer.