In a small measuring cup, dissolve the <em>nigari</em> in the remaining 1/4 cup of filtered water. Spoon 2 tablespoons plus 2 teaspoons of the nigari solution into a large heatproof glass bowl. In a clean large saucepan, heat the soy milk to 185°. Gently pour the hot soy milk into the bowl with the <em>nigari</em> solution and quickly stir once or twice just to combine thoroughly; it's easy to scramble the rapidly coagulating tofu. Cover and let stand undisturbed until the silken tofu is fully set, about 5 minutes. Discard the remaining <em>nigari</em> solution. Serve.