1/4 cup butter (could use a vegan butter like Earth Balance, or ghee)
4 cloves garlic, minced
16oz mushrooms (I've used both white and baby bella mushrooms,) washed then patted dry
salt and pepper
Place a large cast iron skillet into the oven then preheat oven to 400 degrees. If you don't have a cast iron skillet you can use a pie pan or casserole dish - do not preheat either of those.
Add butter and garlic to a small dish then microwave until melted, 30 seconds. Trim ends off mushrooms with a small knife then place cap side down in skillet or baking dish..
Source: Easy Garlic Butter Roasted Mushrooms