Melt 1 tablespoon butter in a large skillet over medium heat. Throw in mushrooms and toss around for 2 minutes, just to start the cooking process. Sprinkle mushrooms with salt. Place mushroom caps face down in a baking dish. Heap cavity with sauteed mushrooms, then sprinkle Gruyere over the top.
Bake at 10 minutes on 325 degrees. Turn on broiler and broil for a couple of minutes, until the top of the Gruyere starts to bubble and slightly turn brown.
Sprinkle minced parsley over the top and serve.