Cook shallot in melted butter until translucent.  Add kohlrabi cubes, plus chicken or vegetable broth to cover.  Bring to boil with a pinch of salt, reduce heat, cover partially, and cook until tender.  Puree in a food processor, then pass through a fine sieve to remove any fibers.  Add heavy cream to taste.  Keep warm without boiling.  Meanwhile, sauté shrimp in a bit of butter until just cooked.  Serve the soup in wide bowls, topped with the shrimp and decorated with herb flowers such as borage, coriander, or chives.