A sophisticated, fragrant soup that went down well at the meal for 20 people the night before our wedding. it can be served hot or cold, but you do need a really good blender and/or use a sieve.

1 medium onion

2 medium leeks

2 spring onions

300g potatoes, peeled and chopped

50g bunch of coriander

4 thick stems of lemongrass

50g butter

150ml milk

salt and pepper

Lemon wedges to serve

• Strip the coriander leaves from stalks. Trim the outer skin from lemongrass, leeks, and spring onions, and top and tail (the bits you'd normally throw away)

• Put coriander stalks and all the above trimmings in pan with 850ml water, and salt. Simmer for 30 minutes. Then strain through a sieve

• Meanwhile finely chop remaining lemongrass, leeks and spring onions

• Melt butter in large pan and gently sweat the lemon grass, onion, leeks and potatoes for 10 minutes

• Add the stock, milk, and chopped coriander leaves. Season and simmer gently for 25 minutes

• Liquidise until very smooth, and chill if you fancy it that way

• Serve with lemon wedges