1.2 litres (2 pints) clear chicken or vegetable stock
2.5 cm (1 inch) piece of fresh root ginger, finely chopped
3 lime leaves, thinly sliced
1 small red chilli, deseeded and finely sliced (optional)
1 tablespoon fish sauce
250 g (8 oz) buckwheat soba noodles
200 g (7 oz) firm tofu, diced
1 spring onion, thinly sliced
2 tablespoons chopped coriander leaves
Finely slice the tender hearts of the lemon grass stalks and place in a saucepan with the chicken stock, ginger, lime leaves, chilli, if using, and fish sauce. Bring to the boil, then reduce the heat to low and simmer gently for 10–12 minutes.
Meanwhile, bring a large saucepan of water to the boil and cook the noodles for 6–7 minutes until tender, or according to the packet instructions. Drain the noodles and divide among 4 warmed bowls.
Scatter the tofu over the noodles and then carefully ladle over the hot, fragrant soup. Scatter over the spring onions and coriander and serve immediately.