In small dry skillet, toast coriander seeds over medium-low heat for 2 minutes. Add fennel seeds, cumin seeds and peppercorns; toast, shaking pan, until lightly toasted and fragrant, about 1-1/2 minutes. Using spice grinder (or coffee grinder wiped clean) or mortar and pestle, grind coarsely.

In small bowl, mash garlic with salt to smooth paste; stir in oil and spice mixture. Rub over meat portion of lamb racks. Marinate for at least 1 hour or refrigerate for up to 1 day (bring to room temperature).

Herbed Potatoes: Reserve 1 tbsp (15 mL) of the oil; in food processor or blender, pulse remaining oil, onions, coriander, mint, jalapeño peppers and salt. Using mandoline or sharp knife, finely slice potatoes. In greased 11- x 7-inch (2 L) baking dish, arrange one-quarter of the potatoes in even layer; spread with one-third of the herb mixture. Repeat twice and top with layer of potatoes; brush with reserved oil. Cover with foil and bake in 400F (200C) oven until potatoes are almost tender when tested with knife, about 1 hour.

Meanwhile, place lamb on roasting pan. Remove foil from potatoes; place lamb in oven. Roast until potatoes are golden brown and lamb is crusty on surface and meat thermometer registers 140F (60C) for rare, 30 to 40 minutes, or until desired doneness. Let stand for 5 minutes.

Cut potatoes into 6 squares; place in centre of 6 warmed dinner plates. Cut lamb into individual chops; place 2 on top of each potato square. Top with coriander sprig if desired.

Makes 6 servings.