1. Whisk together sour cream, mayonnaise, mustard, capers, vinegar, salt, and pepper in a medium bowl.
2. Peel Jerusalem artichokes with a knife and cut into fine matchsticks (you should have about 3 cups); to prevent browning, add them to dressing as you cut them, and stir to coat. Cut carrot into fine matchsticks the same size as artichokes. Gently stir carrot and parsley into salad.