Soak shiitake in 200 ml boiling water until soft. Squeeze, mince, and keep the soaking liquid.
Stir Seasoning A into the shiitake soaking liquid; let cool to room temperature.
In a bowl, add all filling ingredients (start with pork), pour in the seasoned liquid, and knead well until sticky.
Spread ⅓ of the filling in a heatproof dish. Cover the surface with wrappers. Add the rest of the filling, level it, then cover with more wrappers.
Brush the top with the soy-water mix.
Steam on high about 15 minutes (skillet + lid or foil works) until cooked through. Slice like a cake and serve with black vinegar and ginger.
