Preheat your oven to 375°
In a medium bowl, whisk together butter, garlic, thyme, and vinegar.
Evenly spread the mushrooms on a large baking sheet.
Pour the butter-garlic mixture over mushrooms and dash with salt and pepper. Toss to coat then spread back into an even layer.
Roast mushrooms for 15 to 18 minutes, until golden and tender.