Get the pan ripping hot. Add the oil and heat until just smoking. Use a high heat oil like canola or peanut.
Add mushrooms, a generous pinch of salt and brown, stirring/tossing/moving to avoid burning.
When you have achieved the level of brown-ness you desire, you can do either of the following:
1. Turn off the heat and add an appropriately sized hunk of butter (like a tablespoon or so) and swirl around the pan to emulsify. Garnish if desired with minced parsley.
2. Do none of the above and plate as I have pictured here. I am planning to use these for a pizza topping.