To make “Borscht Bisque”, puree soup in batches in a blender until very smooth. For each cup of puree, stir in 1/4 cup sour cream or Greek yogurt mixed with 1 tsp flour. Simmer over very low heat until thickened and smooth, at least 5 minutes. Serve garnished with a drizzle of sour cream or yogurt thinned with cream, and a sprinkling of chives, parsley, and/or dill.