1 Put the noodles into a largebowl. Pour boiling water over then leave for 3 minutes. Drain in a colander.
2 Shell the prawns but reserve the heads and shells to make a stock. Devein the prawns.
3 Put the vegetable oil into a hot wok then add the prawn heads and shells, toss until they turn red. Add 1 cup of water, bring to a boil then cover and simmer for 5 minutes. Strain the stock and return to the wok.
4 Drop the shelled prawns into the simmering stock and leave until they just begin to change colour. Strain again and reserve the stock.
5 Heat the second measure of vegetable oil with the peanut oil in the wok. Fry the beansprouts, shallots, garlic, lemongrass and celery until soft and golden.
6 Add the remaining stock, noodles and prawns. Stir fry for two minutes then serve with plenty of garlic chives and chillies - offering lemon wedges on the side.