Combine 80 ml (2½ fl oz/⅓ cup) mirin (rice wine), 3 teaspoons Worcestershire sauce, 1½ tablespoons soy sauce and 3 teaspoons sugar in a bowl and set aside. Heat 1 tablespoon of sesame oil in a wok over high heat. Add 1 thickly sliced onion, 6 sliced shiitake mushrooms, ½ thickly sliced white cabbage and 250 g (9 oz) thinly sliced pork fillet. Stir-fry for 5 minutes or until the pork is golden and crisp. Add 400 g (14 oz) of cooked udon noodles and toss until heated through. Add the sauce and toss for another minute or until well combined.