Trim the stems of the mushrooms and cut into even pieces (when using button mushrooms I usually cut them into fourths or sixths)
Heat a pan on high dry.
When the pan is hot add enough oil to coat the bottom of the pan lightly.
When the oil starts to shimmer and send up some whisks of smoke add your cut mushrooms. Let them sit for a few minutes without stirring them or seasoning to gain color.
Add a small pinch of salt so the mushrooms release their liquid.
When the mushrooms have released most of their liquid add butter and thyme. Stirring constantly coat the mushrooms in the butter.
Season with salt and pepper and serve