Watercress Soup

2 teaspoons olive oil
1 onion, finely chopped
1 leek, finely sliced
2 cloves garlic, finely sliced
250g potatoes, peeled and diced
200g spinach
200g watercress
1 litre vegetable stock
Sea salt, ground black pepper and freshly grated nutmeg to taste
4 tablespoons natural low-fat yoghurt

Fry the onion and leek in a soup pot until soft.
Add the garlic, potatoes, salt, pepper and nutmeg. Pour over the stock, stir and simmer for 15 minutes until potatoes are soft.
Drop in the spinach, then watercress, pushing into the soup until just wilted.
Whiz in a blender until smooth.
Reheat if necessary and serve with a drizzle of yogurt.