If you want a lovely brown crust on your mushrooms, use high heat (preheated pan of course) and a reasonable amount of oil (or a combination of oil and butter), place your mushrooms in a thin, even layer over the entire cooking surface (it's ok if you have a tiny little bit of stacking - they don't have to be perfectly arranged), and let them sit long enough on one side to form that crust before you redistribute them, then repeat.

That way, the water that is released as they cook is immediately evaporated by the high surface heat, which is much more conducive to the sear you want.

Salting at the very end also prevents an excessive release of moisture during the cooking process.

Enjoy your beautifully browned mushrooms! :)