Pour the sesame seed water through a strainer into a medium-sized pot or saucepan (if using a traditional Japanese strainer, take care not to press down on the mesh as it breaks easily). Once all the water / sesame seed paste has been added to the pot, slowly pour in the kuzu starch and incorporate with a whisk (do this step off the heat).
Using a medium flame, whisk the sesame seed mixture frequently. It will continue to thicken. Bring to a boil and stir vigorously, for about 20 minutes; the mixture will change in both texture and color and become more translucent (especially if using white sesame) and will look like a thick pudding.
Pour the sesame tofu into a square or decorative mold that has been dampened with water or sprayed with nonstick cooking spray (I have made gomadofu with metal, silicone, and plastic molds and all three will work).
Bang on a flat surface to remove trapped air bubbles and smooth the top (don’t worry if there are wrinkles; this will be at the bottom once you unmold).
Let cool to room temperature (this can be done more quickly by placing the mold (in a larger pan and surrounding with ice water) then store in the refrigerator.
Unmold onto a cutting board and slice using a knife dipped in hot water between each cut (if using decorative silicone or plastic molds, simply unmold directly onto your serving dish).
Garnish with grated ginger, wasabi, and a drizzle of soy sauce and enjoy!