Heat the butter in a large frying pan. Fry the mushrooms for 3-4 minutes, turning as they cook. Add 1/2 the spring onions and all the ginger, chilli, soy sauce and sugar. Keep turning the mushrooms in the sauce until they are cooked and the sauce is glossy but still liquid. Cook the basmati following pack instructions then stir through the rest of the spring onions and the sesame oil. Spoon the rice into bowls, add the mushrooms and spoon over the sauce. Finish with a few more chopped spring onions, if you like.