Heat sunflower oil in a pot.

Add sliced onion and cubed potatoes to the pot.

Stir and cook until softened.

Add vegetable stock and milk to the pot.

Season with salt and black pepper.

Bring to a boil, then reduce heat and simmer for 10-15 minutes until potatoes are tender.

Add sorrel leaves and creme fraiche or cream 2 minutes before the end of cooking.

Liquidize the soup using a blender or immersion blender.

Serve hot or chilled.

Garnish with croutons and finely chopped sorrel leaves.

To serve chilled, allow to cool and refrigerate.

Add an ice cube to each bowl before serving chilled.

Garnish as before.