In a large skillet, saute mushrooms in 2 tablespoons butter until tender. Place chicken in a greased shallow 3-qt. baking dish; sprinkle with salt and pepper. Melt remaining butter; drizzle over chicken. Combine broth and sherry; pour over chicken. Spoon mushrooms over top. Cover and bake at 400 degrees F for 20-25 minutes or until chicken is no longer pink.