Beet and orange is a classic combination, but they can be almost cloyingly sweet together. With a bracing dash of buttermilk, you can enjoy the best of this combination but cut some of the sweetness. Sometimes I sprinkle fresh dill on top, for a different flavor profile. It’s a wonderfully refreshing soup on a hot summer night.
Place the beets in a saucepan and cover with water. Bring the pan to a boil over high heat, then lower the heat, cover, and simmer the beets until tender, about 1 hour. Drain and rinse in cold water.
Slip off and discard the skins. Slice the beets coarsely directly into a blender or the bowl of a food processor. Add 1 cup of the buttermilk and process until very smooth.
Pour into a large jug or bowl and whisk in the remaining 1cup buttermilk, the orange zest and juice, and the vinegar to your taste. Season to taste with salt and pepper. Cover and refrigerate until thoroughly chilled, at least 3 hours or overnight. Taste and adjust the seasoning as desired when the soup is cold. Sprinkle with the dill before serving.