Preheat the oven to 200ºC/400ºF/gas 6. Tear the bread into rough 2cm chunks and place in a food processor, then pour over the Prosecco, drizzle with 1 tablespoon of oil, finely grate in the lemon zest and squeeze in the juice. Season generously with sea salt and black pepper, then leave to soak for 10 minutes. Peel the garlic and roughly chop with the chilli, pick the mint leaves, and add to the processor with the anchovies and capers. Pulse into crumbs, then taste and season to perfection, if needed.
Lay the lamb leg on a board, skin side down. Massage all over with a pinch of salt and pepper, then spoon over the stuffing in an even layer. Roll up the leg meat to seal the filling inside, then tie at regular intervals with six lengths of string to make sure the stuffing is secure. Place straight on to the bars of the oven, with a tray underneath to catch the juices. Roast for 1 hour 10 minutes, or until the lamb is golden, yet still blushing and pink in the middle (cook for a further 10 to 15 minutes if you prefer your lamb well done). Rest for 5 minutes, while you simmer the tray of drippings on a medium heat with a little water, stirring to pick up any nice sticky bits. Slice the lamb and spoon over the tray juices. Beautiful served with roast potatoes and seasonal veg – or I love it stuffed into a sandwich.