Puree all ingredients in a blender until smooth. I like to do this in 2 batches, halving the amounts for each batch, so I don't overcrowd the blender cup.
Pour mixture into a freezer safe 9 x 13 dish (baking dish or Pyrex work) and place in the freezer uncovered.
Stir the mixture every 30 minutes as the crystals form, for 3.5 to 4 hours, making sure to scrape down the sides and mix that portion in as well. When the granita is completely crystallized (there is no mixture pooling on the sides uncrystallized), it is ready to serve. You don't want to keep stirring at this point because you might break the crystals down too fine and create blocks. You can keep the granita in the freezer in this state for up to 2 hours before serving.
Spoon into your serving dish, garnish as desired, and enjoy! :)
