Gently wipe the mushrooms with a paper towel and cut into thick ½-inch slices.
In a 10-inch skillet, heat the oil over medium-high heat.
Add the mushrooms and quickly toss to coat with oil. Once coated, allow the mushrooms to cook undisturbed for 4-5 minutes until they brown on one side. Stir and continue cooking the mushrooms until any released liquid has evaporated.
Move the mushrooms to one side of the pan. Add the butter and garlic to the empty side and cook until fragrant, about 1 minute. Sprinkle the thyme leaves over the mushrooms.
Stir garlic butter into the mushrooms and season with salt & pepper to taste. Garnish with parsley.
Notes
To clean mushrooms, do not wash. Simply wipe them with a clean, dry paper towel. This prevents them from absorbing too much moisture.
Keep leftover refrigerated in an airtight container, and use within 3 days.