Heat a large skillet over medium-high heat. Coat pan with cooking spray. Add the mushrooms and thyme to pan; sauté for 4 minutes or until mushrooms are lightly browned. Stir in broth, wine, cornstarch, salt, and pepper; cook 2 minutes or until sauce is slightly thickened. Remove from heat; add butter, stirring until butter melts.
Make sure the sauce is bubbling as it cooks so the cornstarch can effectively thicken it. A couple of tablespoons of butter round out the flavors and add richness to this sauce—stir it in off the heat so it blends in and emulsifies.
This is an excellent sauce to serve with any meat!! I mades the menu with grilled flank steak, garlic mashed potatoes & butter roasted carrots last week & my husband raved as did I. tonight I am making it again to serve over leftover roast pork. Cant wait for dinner!!!