Coarsely chop the sage and rosemary leaves and mix them with the salt. Cover the bottom of a deep oven dish with a thick layer of the salt mixture, lay the meat on top of it, cover with the remaining salt and sprinkle the water over the surface. Put the beef in the oven, preheated to 220 °C, and cook it for 30 minutes if you want the meat to be quite rare; if you prefer it more well done, cook it for 10 minutes longer. Take the roast beef out of the oven, allow it to cool for a few minutes, then break the salt crust and serve.
Cooked in this way the meat maintains its fragrance and aromas to the fullest, and is excellent eaten just as it is. You can accompany it with a sauce (for example mayonnaise, La Cipollina or sun-dried tomato paste) or serve it, quite simply, with a drizzle of extra virgin olive oil.