Lemon Ice Cream and Raspberry Granita Sundaes

Puree raspberries in processor until almost smooth. Transfer to fine-mesh strainer set over medium bowl. Using silicone spatula, press on solids to extract puree. Discard seeds in strainer. Transfer 1/3 cup puree to small bowl; add 2 tablespoons sugar and stir until sugar dissolves. Cover; chill for sauce. Bring 3/4 cup water and 1/2 cup sugar to boil in pan, stirring until sugar dissolves. Cool syrup. Stir syrup into remaining puree in medium bowl for granita. Transfer to 8x8x2-inch glass baking dish. Freeze until mixture begins to set, stirring every 45 minutes to break up large pieces, 2 to 3 hours. Cover; freeze until firm, about 6 hours. DO AHEAD: Sauce and granita can be made 1 day ahead. Keep sauce chilled and granita frozen. Using fork, scrape surface of granita to form crystals. Place scoop of lemon ice cream in each of 2 dessert glasses. Top each with scoop of granita; drizzle with raspberry sauce. Top with scoop of ice cream, then scoop of granita; drizzle with sauce.