Cut slits all over roast; insert 1 garlic sliver into each. Sprinkle with 3/4 tsp/4 mL of the salt and pepper. Lay rosemary sprigs over top; tie tightly at 1-inch/2.5 cm intervals (if roast is already tied, tuck rosemary under strings).

Place roast in heavy-duty resealable freezer bag.

In blender, purée together onion, anchovies and wine; pour over roast. Refrigerate for 8 hours or, preferably, 1 to 2 days, turning occasionally.

Reserving marinade, remove roast; let come to room temperature. Secure rotisserie prong to 1 end of roast; push spit through centre and secure other end with prong.

Grill, covered, on rotisserie over indirect medium heat, basting with reserved marinade every 10 minutes, for 1 hour. Sprinkle roast with remaining salt; grill, without basting, until just a hint of pink remains and centre reaches 160°F/71°C, about 1 hour.

Transfer to cutting board; tent with foil and let stand for 10 to 15 minutes. Remove string and rosemary before carving.

Makes 8 servings.