In a large pan over medium-high heat melt the butter. Add the mushrooms and cook 2-3 until browned and slightly tender.
Add in the garlic and let cook another minute.
Add in the beef stock and deglaze the pan or use the spoon to scrape up any brown bits on the bottom of the then.
Add the heavy cream and parmesan cheese, thyme, salt and pepper. Stir until thickened and mushrooms are nicely coated. Remove from heat and serve immediately as a side dish or as a topping for grilled steak or pork chops.