Combine all ingredients in a blender, except the blueberries and pulse as necessary. Pour the mixture into a shallow baking dish. Stir in the blueberries. Place the dish in the freezer, stir with a fork after 30 minutes. Continue to stir it every hour until completely frozen (about 4-6 hours). Store in an airtight container for up to 5 days.
Optional: Serve the granita on peach "carpaccio". Slice peaches very thinly to build a base on the plate. Brush lightly with maple syrup and top with granita and fresh blueberries.