How to Make It
In a medium pot, combine the sugar and water and bring to a boil, stirring until the sugar is dissolved. Add the carrot tops and parsley, reduce the heat to low, and simmer for 3 minutes, until just cooked. Transfer to a blender, add the lemon juice, and blend for a few minutes to a smooth puree.
Transfer to a shallow metal container at least 8 x 8 x 2 inches, add the vodka (if using), and freeze for 3 to 3 1/2 hours, scraping periodically with a fork so that the granita is evenly frozen.
To serve, crush any remaining lumps in the granita. Fill each of 4 wide shallow bowls with 1/4 cup whipped yogurt and dot the yogurt with the carrot raisins. Top each with 3 heaping tablespoons of the granita.