Watercress and oysters work so well together and here smoked oil adds another amazing taste dimension. If you haven't time to prepare the oil, then use a good-quality olive oil or even my lemon oil (see page 227 of the book). You can also use rocket in place of watercress, or a mixture of spinach and watercress or rocket if you like.
8 oysters, shucked (see page 258 of the book), juices retained
Light rapeseed oil for cooking
1 small onion, peeled and sliced
2 garlic cloves, peeled, green germ removed, and sliced
1 large potato, peeled and thinly sliced
1 litre (approx) vegetable stock (see page 222 of the book)
2 large bunches of watercress, leaves only, washed
Cornish sea salt and freshly ground black pepper
Smoked oil (see page 227 of the book), to serve
Heat a medium saucepan and add a good drizzle of rapeseed oil. Add the onion and garlic and cook for one minute, without colouring. Add the sliced potato and then pour on enough of the vegetable stock to cover. Simmer for about 10 minutes until the potato is cooked. Transfer the contents of the pan to a blender.
Place a frying pan over a medium-high heat and add a little oil. Now add the watercress and fry briefly until just wilted. Add the watercress to the blender and blitz for three minutes or until smooth. Season with salt to taste. Unless serving straight away, chill the soup over ice to retain its vivid green colour.
When ready to serve, pour the watercress soup base into a pan, add the reserved oyster juices and enough of the remaining stock to give the required consistency. Taste and adjust the seasoning. Heat through gently.
Divide the soup between four warmed bowls. Add the oysters and finish each serving with a drizzle of smoked oil to serve.