Tear large mushrooms vertically into two to three portions.
Place all the mushrooms in a large mixing bowl and toss with the salt and pepper.
In a small bowl, beat the egg then pour into the bowl with the mushrooms. Mix well to coat each piece of mushroom with egg.
Dump 1/2 cup of starch into the mushrooms. Mix to distribute evenly. If the mixture appears too be too wet, you may add another quarter cup of starch. For a thicker coating, use all of the starch.
Heat the wok. Pour in enough cooking oil to reach a depth of at least three inches at the center.
When the oil reaches 350F, fry the oyster mushrooms in batches until golden and crisp.
Drain the cooked mushrooms on a rack, cook the next batch, and so on, until all the mushrooms have been fried.
Serve the crispy oyster mushrooms immediately with mayo and ketchup in separate bowls.