The berries' mild flavor is enhanced by fruity wine in a dessert soup; buttermilk adds a tang along with a swirl of elegance.
In a medium saucepan, combine sugar with 2 cups water; bring to a boil over high heat. Add blueberries, wine, and lemon zest; return to a simmer. Cook, stirring, until blueberries begin to burst, about 3 minutes.
Pass mixture through a food mill or a fine sieve into a large bowl, discarding solids. Stir lemon juice into strained liquid. Cover with plastic wrap; refrigerate until completely chilled, about 1 1/2 hours.
Divide soup among six bowls. Swirl about 2 tablespoons buttermilk into each bowl, and serve immediately.
Adding extra lemon juice in step two will give the soup more tartness. Serve it thoroughly chilled, accompanied by tuiles, biscotti, or other crisp cookies.