Preheat your oven to 450° on convection if you have it.
Clean the mushrooms by wiping them with a paper towel or a quick rinse.
Spread your mushrooms on a baking sheet without crowding them.
Add the olive oil and butter to a small bowl and microwave until the butter is melted.
Add the dry seasonings and minced garlic to the butter and stir to combine
Drizzle the butter mixture over the mushrooms and toss well.
Turn most of the mushrooms with the cut side down so the liquid can drain off.
Place the pan in the oven and cook for 20 – 25 minutes, stirring at the 15-minute mark.
When the mushrooms are golden brown, remove them from the oven.
Transfer the mushrooms to a serving bowl and garnish with a few sprigs of fresh thyme, if desired.