Soothing Asian broth with shimeji mushrooms and noodles

In a medium pot, place 6 roughly chopped lemongrass stalks, 4 sliced thumbs ginger, 3 whole-peeled garlic cloves, 4 bruised fresh lemon leaves (optional), 1 seeded red chilli, 10ml (2 tsp) sesame oil, 1 peeled and quartered onion, juice of 1 lime, 60ml (¼ cup) soya sauce and 1,5L vegetable stock. Simmer for 30 minutes. Pass the liquid through a sieve and return to the pot, discarding the bits. Bring to a simmer again and add 150g shimeji mushrooms, 100g dried wholewheat noodles and 100g baby bok choi. Simmer for a further 7 minutes before dividing between 2 bowls and sprinkling with fresh coriander and chopped spring onion. Serve with lime wedges for squeezing.