Pour mollases (light - 40% reduced sugar) into a small frying pan. Add minced garlic, shallots, a good balsamic vinegar and Kikkoman shoyu (soy sauce), salt and fresh black pepper. Render sauce for a few minutes, add roughly chopped white onion and thinly sliced portobello or cremini mushrooms. Cook over a medium heat to reduce further for a few minutes. Pour over blocks of cotton (firm) tofu to marinate for several hours.
Bake whole blocks of tofu in a 400 degree oven for 20 minutes, basting with the glaze twice to create a thick coat. Cut the tofu into 1/4 inch slices, cleaning the knife between slices. This will produce a black exterior crust which soaks into the edges of the tofu yet leaving a snow white core.