Put ⅓ cup rosemary leaves, 3 tablespoons of the oil, 5 of the garlic cloves, 8 of the sage leaves and 1 teaspoon of salt in the work bowl of a mini food processor. Process until you have a smooth paste.

Lay the loin on your work surface fat-side down. Cut along the top side of the “tail” and into the eye of the roast, ‘unrolling’ the loin into a rectangle of more or less even thickness, pounding with a mallet to flatten and even it out.

Spread the herb paste evenly over the entire cut surface of the pork. Roll the roast into a compact roll with a spiral of the herb filling running through it. Tie the roast securely at 1-inch intervals with kitchen twine.

Combine the ground fennel, orange zest, 1 teaspoon salt and a generous grinding of black pepper in a small bowl and rub all over the surface of the roast.

Set the loin in a heavy flameproof casserole into which it fits snugly. Add the rosemary sprigs, remaining 8 sage leaves and the remaining 5 garlic cloves. Pour in just enough water to come halfway up the sides of the meat and add the orange juice.

Season the water lightly with salt and pepper. Bring to a boil over high heat, lower the heat so the pork is simmering and cook, partially covered and occasionally turning the pork in the liquid, until almost all of the water has evaporated and the meat begins to stick to the casserole, about 1 to 1 ½ hours.

Skim the foam that rises to the surface regularly as the pork simmers.

Pour or spoon off the fat remaining in the braising pan and pour in the remaining 3 tablespoons of olive oil. Adjust the heat to very low.

Cook, turning often, until the pork has a caramelized, golden brown crust, about 15 minutes.

To serve hot, as a main course, let the porchetta rest 20 minutes, remove the strings, then slice ¼-inch thick. Porchetta can also be served warm or at room temperature.