1. Warm the olive oil in a casserole type pan over medium heat and stir fry the spring onions for 2-3 minutes until translucent.
2. Cut the broccoli into even-sized florets and chop the stalks into small pieces. Add them in along with the vegetable stock. Put the lid on and simmer over low heat for 20 minutes until the broccoli are soft. Then pour the whole lot into a liquidiser and whiz to a smooth puree. Season with salt and pepper and keep the soup warm.
3. Array the prosciutto slices onto a baking tray lined with greaseproof paper. Bake at air220ºC for 10 minutes until crispy. Place the slices on some kitchen paper and let them cool completely.
4. Divide the soup into 4 plates. Garnish each plate with a grated prosciutto slice and serve with yoghurt.