Method:
1 Heat a little oil in a saucepan. Add onion and garlic and cook until soft. Add the watercress and cook 2-3 minutes until wilted. Remove from the heat and stir in the stock.
2 Pour the watercress mixture into blender. Add ice cubes and cream and blend until smooth. Season with salt and pepper.
3 Pour into serving bowls. Top with dollop of yoghurt. Sprinkle with pepper. Serve.