Pour the pre-made sangria into a shallow, flat bottomed container. A metal container will freeze the mixture faster than a glass or plastic container of the same size
Put the container in the freezer
After an hour scrape the frozen or mostly frozen sangria with a metal fork and mix it around. Return the pan to the freezer
Continue to scrape and stir every 30 minutes or so for 4 hours
Scoop the sangria granita into a glass or bowl and add fruit
Serve immediately or cover with plastic wrap and store in the freezer for up to 2 days