2 pints (4 cups) fresh or frozen raspberries, thawed
1 cup minus 2 tablespoons sugar
1/2 teaspoon fresh lemon juice
1/4 teaspoon kosher salt
4 cups cold seltzer water
1 pint strawberry ice cream
1/4 cup fresh blueberries
1/4 cup fresh boysenberries, blackberries, or raspberries
How to Make It
Purée raspberries in a food processor. Strain through a fine-mesh sieve, discarding seeds (should yield about 2 cups purée). In a large pitcher, mix the purée, sugar, lemon juice, and salt (you can make the purée up to 12 hours before serving; just keep refrigerated). Add the seltzer and stir until combined.
Place a few small scoops of ice cream and some blueberries and other berries in each of 6 glasses. Fill with the soda. Serve with long spoons and straws.