Mix potato starch and some water and knead. Add the sesame seeds paste, starch mixture and salt to kelp soup and mix well. Cook over medium heat, stirring constantly. Pay careful attention to avoid burning.
When the mixture become thick, turn lower the heat and cook for 15 or 20 minutes, until the mixture become clear and heavy.
Pour the mixture into a wet gelatin mold, level the surface and let it cool. When cooled, chill in a refrigerator or chilled water.
When it is chilled, cut in 4 pieces and serve on individual plates. Garnish with wasabi.