How to Make It
Soak the mushrooms in 1 cup of warm water until soft, 10 to 15 minutes. Drain and discard the stems. Finely dice the mushroom caps.
Heat the oil in a medium skillet. Add the bok choy, minced scallions and ginger and sauté over moderately high heat until wilted. Stir in the mushrooms. Transfer to a bowl and let cool. Stir in the ricotta, egg yolk, pepper and 1/2 teaspoon salt.
Bring a medium pot of water to a boil; stir in 1 tablespoon salt. Dip the wonton skins in the water one at a time and then spread them out on a clean towel.
Preheat the oven to 350°. Using a pastry brush, grease an 8-by-11-inch baking dish with some of the melted butter. Spoon 1 tablespoon of the vegetable filling into the center of each wonton skin and roll up to form a log. Place the cannelloni in a single layer, just touching, in the prepared baking dish. Drizzle with the remaining melted butter and 2 tablespoons of the Mushroom Broth. Bake the cannelloni for 10 minutes, or until cooked through.
Place 3 cannelloni in each soup plate and spoon 1/4 cup Mushroom Broth around each serving. Garnish with the sliced scallions and serve.
In a small bowl, soak the dried mushrooms in 2 cups of warm water until soft, 10 to 15 minutes.
Heat the oil in a heavy medium saucepan. Add the shallots and cook over moderate heat until wilted, about 2 minutes. Add the white mushrooms and ginger. Stir in the dried mushrooms and their soaking liquid along with 6 cups of cold water. Bring to a boil, then simmer over moderate heat until the broth is reduced to 4 cups, about 40 minutes. Strain the broth.