Melt the salted butter in a large, nonstick skillet over medium-high heat.

Add the sliced mushrooms and kosher salt to the skillet. Stir to coat in the butter, and spread the mushrooms out in an even layer.

Allow the mushrooms to cook, WITHOUT STIRRING, for about 5 minutes, until much of the liquid has evaporated.

Stir the mushrooms, trying to flip them over, and spread them in an even layer again. Allow to cook for another 2-3 minutes without stirring.

Stir one more time and allow to cook for another 2-3 minutes, until mushrooms are deeply browned and there is almost no liquid in the pan.

Adjust seasoning if needed, adding black pepper if desired. Serve as is or use in other recipes.