Pea and leek soup with basil oil

Ingredients

2 tbsp olive oil
20g unsalted butter
3 leeks, trimmed and finely sliced
4 shallots, peeled and finely sliced
2 garlic cloves, peeled and finely sliced
2 sticks celery, finely sliced
2 bay leaves
Salt and white pepper
800g podded peas
1 litre water
4 heaped tsp crème fraîche, to serve

For the basil oil:
2 bunches basil, leaves picked
½ clove garlic
About 100ml olive oil

Serves four

A wonderful, luminous-green soup. If you like, simplify the method: instead of basil oil, finish with shredded basil or mint and a drizzle of oil; and miss out passing it through a sieve - it'll be less smooth, but still delightful.

First make the basil oil. Put the basil leaves, garlic, some salt and pepper in a small food processor bowl, turn on the machine and add the oil in a slow stream until you have a runny purée consistency. The oil will keep in the fridge for a few days.
Next, turn your attentions to the soup itself. Heat the oil and butter in a large pot, then add the leeks, shallots, garlic, celery, bay leaves, some salt and white pepper, and sauté over a low heat for 20 minutes, stirring occasionally - it is important that you give it at least this amount of cooking time, to allow the natural sweetness of the vegetables to come out; make sure, though, that they do not take on any colour.
Add the peas and water, bring to a gentle boil and cook for five minutes, just lightly to cook the peas. Remove from the heat, remove and discard the bay leaves, and use a blender to process the soup as fine as you can.
Transfer the soup to a fine sieve, then take your time to pass it through thoroughly - use the back of a ladle to press the mushed-up vegetables through the sieve, rubbing them vigorously on the inside of the sieve. You want to end up with a totally dry pulp in the sieve, which you can then discard.
Transfer the soup to a clean pot and reheat gently. Taste and adjust the seasoning. To serve, pour the soup into serving bowls and finish with a drizzle of basil oil and crème fraîche on top.