Dry roast 2 tablespoons kosher salt with 5 tablespoons Szechuan peppercorns in dry skillet on moderate heat. Stir with wooden spoon until aromatic and slightly browned. Do not burn; watch carefully. Place in container of food processor with 2 tablespoons of free flowing light brown sugar, and 1 ounce package of dried porcini mushrooms. Grind as finely as possible. (Note: Szechuan peppercorns are available in most Chinese grocery stores. I find it easier to get a 9 ounce jar ordered on the Internet, www.spicebarn.com).
Leftovers can be stored in container. Use a tablespoon or so of rub mixture in other gravies and sauces; it stays good forever.