In a mixing bowl, cornstarch, soy, dry sherry, molasses, salt, oil. Stir to combine very well, add chicken, mix all together, cover and refrigerate.
Put mushrooms in a heatproof bowl, pour boiling water to cover. Cool, squeeze out excess moisture, cut away roots, slice in half.
To assemble—may be done the day before. In an attractive 9” diameter heatproof platter with sides, spread the chicken in an attractive layer. Then make a circle near the outside with the sausage. Make a circle of mushrooms an inch in from the sausage. Repeat till you have no more sausage or mushrooms.(I don’t like putting plastic wrap or aluminum directly on food. Here, make a 9” circle of wax or parchment paper, spread over the chicken and sausage, then cover with plastic wrap. Store in refrigerator.) In a Chinese steamer with at least 5” of boiling water in the bottom, place the top level of the steamer, with the uncovered chicken sausage platter. Steam strongly for 1 ½ hours. Carefully remove the chicken platter and serve it on an adequate-size, stable trivet.
Decorate when you put dish out, with shredded scallion greens and, if you like, cilantro leaves.