Brush radish thoroughly under cold water, drain and peel thinly. Grate on a medium-fine raw vegetable grater. Place in a large enough bowl. Cut hazelnut kernels into flakes and sprinkle on top.
Stir sour cream through with oil, salt, vinegar, pepper and sugar in a small baking bowl, pour over lettuce and fold loosely. Speaking of which, you can also offer radish salad in portions on lettuce leaves or arranged in hollowed out tomatoes as a fancy entrée