Remove the Prosciutto di San Daniele from your refrigerator and bring to room temperature for half an hour.
Melt butter in a heavy based soup pan over a medium high heat. Cook the broccoli florets, leek and garlic for 5 minutes, until they begin to soften.
Add the watercress and cook for a further minute.
Add the vegetable stock and the Grana Padano cheese rind.
Turn the heat down to medium and pop the lid on the pot. Simmer gently for 15-20 minutes, until the vegetables are very tender.
Puree with a hand blender until smooth and then stir in the double cream.
Drizzle a little good quality olive oil over a piece of cooled sourdough toast and top with Prosciutto di San Daniele.
Serve immediately with freshly grated nutmeg and some extra Grana Padano cheese sprinkled over the top of the soup.
The soup recipe can be frozen after pureeing but before adding the double cream. Simply defrost, heat and add the cream. Grana Padano cheese rinds can also be frozen, so don't discard them after you've finished with the rest of the cheese. Simply pop into the soup mix from frozen.