Heat a large skillet (preferably stainless steel or cast iron) over medium heat and add butter. Once melted, add mushrooms to skillet in single layer.
Let the mushrooms cook without stirring them for 5 minutes. Stir and cook for another 3 minutes.
Add brown sugar, stir well, and let cook for 2 minutes.
Add garlic and pepper and cook for one more minute. Toss with chopped parsley and serve.