Preheat broiler. Place chops on the unheated rack of a broiler pan. Sprinkle lightly with salt and pepper. Broil 3 to 4 inches from the heat until done (160 degrees F), turning meat over after half of the broiling time. For veal, allow 14 to 16 minutes for medium; for pork allow 9 to 12 minutes.
Meanwhile, for sauce, in a medium saucepan cook mushrooms and onion in hot butter until tender. Stir in flour and, if using, dried thyme. Add half-and-half all at once. Cook and stir until thickened and bubbly. Cook and stir for 1 minute more. Stir in wine and, if using, fresh thyme. If desired, season sauce with salt and black pepper. Transfer chops to a serving platter. Spoon some of the sauce over the chops. Pass any remaining sauce.