Mix 18 of the raspberries with 2 tablespoons of the raspberry liqueur and freeze. Puree remaining raspberries with remaining ¼ cup liqueur in a blender. Strain out seeds and freeze puree. (Can be prepared a couple of days in advance.)
When ready to serve, spoon a portion of puree into each flute. Top with sparkling wine and drop in 3 frozen raspberries and portion of the liqueur. Serve.
Recipe by Three Many Cooks at https://threemanycooks.com/recipes/raspberry-ice-bellinis/