- 1 3/4 cups milk
- 3/4 cup heavy (whipping) cream
- 2/3 cup water
- 1 cup sugar
- 1/3 cup light corn syrup
- 1/8 teaspoon kosher salt
- 1 1/2 pints (3 cups) fresh blackberries
- 3 tablespoons crème de cassis
- 1 teaspoon freshly squeezed lemon juice
- 2 small fresh pineapples
- 6 tablespoons sugar, plus more as needed
- Large pinch of kosher salt
- 3 cups cold seltzer water
- 2 cups ice cubes
- In a bowl, whisk together the milk, cream, water, sugar, corn syrup, and salt in a medium heavy saucepan. Cook over medium heat, stirring occasionally, until almost simmering. Transfer the mixture to a bowl and cool over an ice bath until room temperature.
- Purée the blackberries in a food processor. Strain the purée through a medium-mesh, then a fine-mesh sieve, discarding the seeds. There should be 3/4 cup pure. Stir the purée, cassis, and lemon juice into the cream. Refrigerate for 4 hours, or up to overnight. Churn in an ice cream machine according to the manufacturer's instructions. Freeze the sherbet until scoopable, about 4 hours, depending on your freezer.
- Remove the rind from the pineapples. From the top, cut the pineapples into quarters. Remove and discard the core. Cut the pineapple flesh into 1-inch pieces. Purée in a food processor until smooth. Strain through a medium-mesh sieve, discarding the pulp. There should be about 4 cups pure. Refrigerate the pure for at least 30 minutes or up to 24 hours.
- Put the pineapple purée in a large pitcher. Stir in the 6 tablespoons sugar and the salt. Taste for sweetness, adding a little more sugar if necessary. Stir in the seltzer water. Grind the ice in a food processor until it has the consistency of shaved ice. Divide the ice among eight 12-ounce glasses. Fill with pineapple soda. Put several scoops of cassis-berry sherbet in each glass. Serve immediately, with straws and long spoons.
- The pineapple purée can be made a day ahead and refrigerated. Mix it with the seltzer just before serving.