Preheat oven to 200°C Season beef with salt and pepper. Using the tip of a sharp knife, make 8 incisions about 2cm deep around the beef. Push a sliver of garlic into each cut.
Lay prosciutto slices overlapping side by side on a chopping boar lined with baking paper. Arrange sage leaves over the top. Put beef at one side and, using the baking paper as a tool to lift and roll, roll to wrap in prosciutto. Tie with butchers twine to secure, Drizzle with olive oil and put in a large roasting pan.
Roast, turning often, for 1 hour or until prosciutto is well browned and meat is cooked to medium. Rest meat in a warm place, loosely covered in foil, for 5 minutes.