Nettles and spinach are so healthy you can almost taste the rich healthy flavor. Despite their richness on nutrition, nettles are not common in cooking. If you have them in the garden, this is a fine way to get rid of them. Use gloves! Alternatively, use spinach only.
The nettle and spinach soup: Remove the stem from the spinach and nettles. Transfer to a medium pot, add stock and cream, and place over medium high heat. Bring to the boil and let it simmer for 10 minutes until entirely collapsed, and the nettles thoroughly unarmed. Transfer the soup to a blender and purée until smooth. Return to pot and reheat over low heat. Add salt to taste. Transfer to serving bowls, and sprinkle with nutmeg and rosemary.
Using your hands, clean the fish, removing any skin and bone. Cut the fish in bite-sized pieces, and arrange on top of the soup. Drizzle with yoghurt, and serve right away.