Puree the soup by transferring to a blender in small batches or use an immersion blender directly in the pan. (If using a regular blender, return the pureed soup to the pan.)
Reduce the heat to low and whisk in the sour cream and tarragon.
½ cup sour cream, 1 tablespoon chopped fresh tarragon
Garnish each with a dollop of sour cream and a little tarragon if desired.
Notes
Any leftover soup will keep for 3 or 4 days in a closed container in the refrigerator. May be reheated in the microwave or over low heat on the stovetop.
This soup also freezes well. Store in a freezer-safe container for up to 3 months. Thaw overnight in the refrigerator before reheating.