In the bowl of a blender, purée berries. Strain berries through a fine-mesh sieve to remove seeds; this will yield about 2 cups of liquid. Set aside.
In a large glass measuring cup, add ¼ cup lemonade and sugar and muddle in basil leaves; let sit for a few minutes before straining and discarding basil. Add remaining lemonade to cup and stir. In a large glass bowl, combine blackberry liquid with lemonade and stir.
Spread across a 13-by-9-inch metal baking pan and cover with aluminum foil; transfer to freezer.
Using the back of a fork, scrape and stir every 30 minutes for at least 2 hours and 30 minutes.
Garnish with remaining basil leaves and serve.
Granita: Cocktail Version
In the bowl of a blender, purée berries. Strain berries through a fine-mesh sieve to remove seeds; this will yield about 2 cups of liquid. Set aside.
In a large glass measuring cup, add ¼ cup lemonade and sugar then muddle in basil leaves; let sit for a few minutes before straining and discarding basil. Add remaining lemonade to cup and stir. In a large glass bowl, combine blackberry liquid with lemonade and vodka and stir.
Spread across a 13-by-9-inch metal baking pan and cover with aluminum foil; transfer to freezer.
Using the back of a fork, scrape and stir every 30 minutes for at least 3 hours.
Garnish with remaining basil leaves and serve.
Notes
- Cocktail v. Mocktail: since the cocktail version has alcohol, it is slightly harder to freeze. This can make it easier to be slushy, but longer to freeze versus the mocktail. - Pan size: A shallower pan is a shorter freeze time and makes it easier to scrape out with a fork. However, a loaf pan would make it frozen solid in the middle and almost impossible to scrape directly out of the freezer.