Start heating the oil in a medium saucepan over medium-high heat.

Lightly whisk the the flours, water and salt together. Prepare a plate with a layer of paper towel for the fried mushrooms.

Add the wasabi and soy to two dipping dishes.

When the oil is 180c, start frying the mushrooms. Dip one oyster mushroom in the batter, let the excess drip off and add it gently to the oil, being careful not to let it splash. Repeat with 2 or 3 more mushrooms. If you add much more than this to the pan, the oil temperature will drop and the food will absorb the oil, rather than just crisping the outside. When food is added to oil at the correct temperature, the water in the food turns to steam instantly and the escaping water forms a barrier which stops the oil being absorbed. Fry the mushrooms in batches and drain on the paper towels. Serve immediately.