Preparation: 10 minutes Cooking: 20 minutes Serves: 5
1.5 onions, diced
3 cloves garlic, peeled and crushed
3 medium potatoes, peeled and sliced
1 vegetable stock cube
125ml double cream
75g unsalted butter
Salt and pepper
1 tbsp olive oil
2 litres boiling water
Heat the olive oil in a large saucepan and add 25g of the butter. Once the butter starts to foam, throw in the onions and garlic with a good pinch of salt and fry until softened and beginning to caramelise.
Add the water to the pan, followed by the potatoes and vegetable stock. Bring to the boil and simmer until the potatoes are cooked through.
Add in the watercress and bring to the boil as quickly as possible. Simmer for 30 seconds then remove from the heat. Use a sieve or slotted spoon to transfer the watercress, onions and potatoes to a blender, in batches if necessary, then use a jug to add enough hot stock to cover. Do not pour everything into the blender at once as the soup may end up too thin. Blend thoroughly.
Blend the cream and butter into the final batch, then whisk everything together. Add salt and pepper to taste.