Move oven rack to middle position and heat oven to 425°F.
For white or brown button mushrooms, leave small ones whole, cut medium ones in half and large ones into quarters. For larger mushrooms like oyster, shiitake or portabella, slice them about 1/4 to 1/2" thick, removing tough stems.
Place sliced mushrooms in a large bowl. Add 1/4 cup olive oil, 1/4 cup unsalted butter, minced garlic, 1 1/2 teaspoons kosher salt, 1 teaspoon smoked paprika, and 1/2 teaspoon freshly ground black pepper. Toss well until mushrooms are evenly coated.
Transfer mushrooms to a large baking sheet. Bake for 30-45 minutes, stirring every 10 minutes, until mushrooms are well browned and wrinkly. Serve immediately or at room temperature.
Notes
To make this recipe vegan and/or dairy free, use a dairy free butter alternative in place of the butter, or simply replace the butter with 3 Tablespoons extra olive oil.