In a large skillet, heat the butter over medium heat.
When the foaming subsides, add the sliced mushrooms, minced garlic, kosher salt, black pepper, and dried thyme.
Cook, stirring often, over medium heat, until the mushrooms are tender and the liquids they release have evaporated, for about 7 minutes.
Garnish the mushrooms with chopped parsley. Serve immediately.
Video
Notes
The most important tip I can give you is to be generous with the butter and stay patient. Mushrooms are best when cooked in lots of fat, over medium heat, slowly and patiently, until very tender. That's when the mushrooms release their flavor.
It's best to wipe the mushrooms clean with damp paper towels. If you prefer to wash them, do so quickly (don't soak them) and dry them well right after washing.
You can keep the leftovers in an airtight container in the fridge for 3-4 days. In fact, they tend to become even more flavorful after a day or two! You can reheat them, covered, in the microwave at 50% power. You can also freeze the leftovers for up to three months. Thaw them overnight in the fridge before reheating them.