1-2 tablespoon Butter (the real thing)
In a non-stick fry pan heat the butter and oil over a medium heat. Add mushrooms and onions and saute till the liquid from the mushrooms begins to evaporate. Add the salt, sugar, and soy sauce. Stir thoroughly, and serve.
This is absolutely the best way to taste test a new mushroom. All the other ingredients enhance the flavor of even the strongest flavored mushroom, without overpowering the most mild. Other subtleties should not be overlooked. First, there is no substitute for real butter, no matter how good your imagination is. Second, use of a cast iron skillet, for instance, will destroy the seasoning on the cast iron. Lastly, this process ensures the mushrooms will be thoroughly cooked, as is recommended because of the indigestible content of mushrooms.