Buttermilk balances the pure sweetness of mulberries, making a not-too-sweet frozen treat.
'mulberries' on Serious Eats
Mulberries are a smaller, less tart cousin of the blackberry, and can be foraged from mulberry trees which grow in residential area of cities in the northeast. If you have access to these bountiful (and free!) berries, try them in this jam, which brings out their earthy, sweet flavor.