Blueberry Ice Cream Sandwiches

In a saucepan over medium-high heat, combine berries, sugar, and salt; cook, stirring often, until sugar dissolves, 3 to 4 minutes. Bring to a boil, reduce heat, and simmer 2 to 3 minutes. Add lemon juice. Puree cooked berries in batches, filling blender no more than halfway each time. Strain into a bowl; refrigerate until chilled. Stir milk and cream into berry mixture. Pour into ice cream maker, and freeze according to manufacturer's instructions. Transfer to freezer until firm enough to hold its shape, about 30 minutes. To assemble, spread about 3/4 cup ice cream on one graham cracker; top with another cracker. Press lightly, and freeze again until firm.