Simple and simply fabulous, this favorite two-ingredient side dish is a no-brainer. For best results, use a 12-inch cast iron skillet.
Preheat a 12-inch cast iron skillet on the stovetop for five minutes over high heat. Meanwhile, wipe any dirt off the mushrooms with a paper towel. Remove stems from shiitakes and oyster mushrooms and trim a slice of the stem end off the baby bellas. Slice baby bellas and shiitakes about 1/4-inch thick and cut oyster mushrooms into small bite-sized pieces.
Add butter to pan. When melted and bubbly, add mushrooms and toss to coat. Cook, stirring only occasionally, for about 10 minutes, until well browned in plenty of spots. Stir in salt and pepper to taste and garnish with parsley if you like.