Combine all the ingredients of B in a mixing bowl. Strain and set aside for 1 hour.
Squeeze dry the soaked mushroom and dice them in small cubes.
Heat 2 tbsp. of oil in the Instant Pot. Press Saute and saute the chopped garlic and shallots. Stir fry the mushrooms, dry prawns, and lap cheong until fragrant. Remove half for the topings and set aside.
Add the yam into the inner pot. Stir fry then add in batter B. Saute on Low and keep stirring until slightly thickened. Press Cancel.
Transfer the batter into an oiled 7-inch stainless steel or bakesafe container. Level the surface.
Cover the lid and select Steam mode on High Pressure and High Heat for 15 minutes. Naturally release pressure when done cooking.
Let the yam cake cool before transfering into a plate. Garnish and serve.