This is a vibrantly flavoured, creamy green soup. I like to serve it cold, although it is equally good as soon it is made. Vary the herbs as you like – coriander, chervil and fennel are other favourites – aiming for 180g-200g in total. Without the herbs, this recipe can be used as the base for lots of other soups.

Serves 6

100g butter
400g onions, chopped
225g potatoes, peeled and diced
1.3 litres stock (preferably homemade chicken)
200ml semi-skimmed milk
60g rocket
45g basil
20g mint
60g parsley
½ lemon, juiced
150ml double cream
Sea salt and freshly ground pepper
A handful of chives or some sprigs of chervil (optional)

Melt the butter in a large, heavy-based pan. Sauté the onions and potatoes on a medium-low heat for about 30 minutes, until the onion is soft and the potato is cooked. (If you have waxy potatoes that are reluctant to soften, add about 300ml of the hot stock and boil until the potato is cooked.)

Liquidise the onion and potato with about 300ml of the stock, then pour it back into the pan and add the rest of the stock and the milk. Bring back to the boil and boil for 1 minute.

Chop the herbs finely together (this is best done in a processor), then stir into the soup. Turn off the heat. Stir in the lemon, then the cream. Season to taste – expect to be generous. Once cold, chill the soup before serving, or serve immediately, snipping chives on top or adding a sprig of chervil, if using.

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