Preparation

Brine the pork

• In a 3- to 4-quart saucepan, combine the salt, sugar, garlic, and herb sprigs with 2 cups of water. Stir over high heat just until the salt and sugar dissolve. Add 6 more cups of water and cool to room temperature. Transfer to a large container, add the pork, cover, and refrigerate for 8 to 18 hours.

Make the herb paste

• Put the garlic, rosemary, sage, 1 Tbs. salt, and 1 tsp. pepper in a large mortar and pound to a coarse paste with the pestle. Add the oil and use the pestle to work it into the garlic paste. If you don’t have a mortar and pestle, combine all the ingredients in a mini food processor and pulse into a coarse paste.

Butterfly and season the pork

• Remove the pork from the brine and pat it dry (discard the brine). Butterfly the pork loin by making a horizontal slit down the length of the loin, cutting almost through to the other side. Open the meat like a book. Spread half of the herb paste over the inner surface of the roast; then fold it back to its original shape. Tie the roast at 1-inch intervals with butcher’s twine and then spread the remaining herb paste over the entire outer surface.

Grill the pork

• Set up a grill for indirect rotisserie cooking according to the manufacturer’s instructions. Heat the grill to 350°F. When ready to cook, skewer the roast lengthwise on the rotisserie spit and let it rotate on the grill, covered, until an instant-read thermometer inserted near the center of the roast registers 145°F, 35 to 45 minutes.
• If you don’t have a rotisserie, set up your grill for indirect grilling. Heat the grill to 350°F. Put the roast in the cool zone on the grill, and cook as directed above, turning the roast about every 10 minutes.
• Remove the roast from the spit if necessary and transfer it to a cutting board. Let stand for 5 minutes, remove the string, and slice thinly. Serve hot, warm, or at room temperature.

Make Ahead Tips

The pork must be brined 8 to 18 hours ahead. You can also butterfly and season the roast with the herb paste up to 4 hours before grilling. Refrigerate, but let sit at room temperature while you heat the grill.