Special equipment: a 12-cube ice cube tray, preferably one that makes square cubes; a freezer-safe pitcher; a large serving spoon
Make the ice: Fill each compartment of a 12-cube ice cube tray about a third of the way up with water and freeze until solid, about 1 hour. Puree half of the raspberries in a food processor until smooth. Add 1 to 2 teaspoons of puree to each cube compartment, coming about another third of the way up the side. Freeze until solid, about 1 hour. Top off each compartment with water and freeze until solid, another hour.
Make the cocktail: Carefully pour the grenadine into a large freezer-safe pitcher so that the grenadine doesn't splash sides. Freeze until the grenadine is very cold and thick, about 30 minutes. Place a large serving spoon in the pitcher, holding it so the tip of the bowl touches the side of the pitcher just above the grenadine line. Slowly pour the orange juice into the bowl of the spoon, filling it up and letting the orange juice overflow run on top of the grenadine without mixing. Slowly bring the spoon up as the orange juice level rises. Using the same technique, add the sparkling wine, stopping after you've poured about half of the bottle to let the fizz subside. Continue pouring, slowly bringing the spoon up as the wine level rises. Top with half of the remaining raspberries.
To serve, stir to combine the cocktail in the pitcher. Add the prepared ice cubes to Champagne flutes. Fill with the cocktail and top off with the remaining raspberries.
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