Mushroom Crusted Prime Rib Roast Ingredients the prime rib: 1 tablespoon dijon mustard 1 tablespoon white miso paste 1 tablespoon oil 2 teaspoons thyme, chopped 2 cloves garlic, chopped 2 teaspoons black pepper, coarsely ground 1 (4 pound) prime rib roast with bone and cap 1 ounce dried porcini mushrooms, chopped into small bits For