1 14-ounce package firm water-packed tofu, cut into 1-inch-thick slabs
6 dried shiitake or Chinese black mushrooms
1 cup hot water
2 cups reduced-sodium chicken broth
2 tablespoons reduced-sodium soy sauce
1 1/2 tablespoons oyster sauce
1 tablespoon Shao Hsing rice wine or dry sherry (see Notes)
1 teaspoon sugar
1 teaspoon canola oil
1 medium leek, white part only, halved lengthwise, rinsed well and cut into 1-inch lengths
1 tablespoon minced garlic
8 ounces white mushrooms, trimmed and halved
4 ounces fresh shiitake mushrooms, stemmed and halved
1 tablespoon cornstarch mixed with 2 tablespoons water