Put the silken tofu and soy sauce in a tall jug and add 3 tablespoons of the reserved pasta water. Use a stick blender to blend to a smooth sauce, then pour into the pan with the mushroom mixture.
Cover with a lid and bring to a simmer. Then, reduce the heat and simmer gently with the lid on for 15 minutes, or until the pasta is tender and the sauce is thick, stirring regularly. Stir more ...