Mix yoghurt and milk in a bowl and season with salt, pepper and a little lemon juice. Wash the herbs, dab dry and pluck off the leaves, except for a parsley stalk.
Puree the herbs and 3 tablespoons of yoghurt milk with a hand blender. Put the yoghurt milk in a plate. Add herbal yoghurt with a spoon in streaks and sprinkle with chilli flakes. Garnish soup with a parsley stalk.