How to Make It
Combine 1 cup water and sugar in a saucepan, and bring to a boil, stirring until sugar dissolves. Remove from heat, and cool completely.
Place the raspberries in a blender, and process until smooth. Press raspberry purée through a sieve into a medium bowl, and discard seeds. Stir in the sugar syrup, 2 cups water, and liqueur. Pour the mixture into an 11 x 7-inch baking dish. Cover and freeze 8 hours or until firm. Remove mixture from freezer; let stand 10 minutes. Scrape entire mixture with a fork until fluffy.