Add all the marinade ingredients to a bowl and whisk until smooth and lump free. Taste and adjust as needed. The marinade should be sharp, salty and intense. Let stand while you prepare the lamb leg.
Place lamb leg on a plastic board and remove the netting. Pat it dry on both sides. Dry meat helps the marinade cling better. Unfold the leg and trim any excess fat on both top and bottom if you prefer, or have your butcher do it for you.
Spread half of the marinade over the bottom of the lamb leg and work it into every crease. Flip the leg and coat the other side with the remaining marinade, making sure you reach all the nooks and crannies. Cover and marinate overnight, refrigerated (at least 8-10 hours).
The next morning, bring the lamb out of the fridge and let it rest at room temperature for 1 to 1.5 hours. Shape the meat into a firm, even log or simply tuck in the edges to create a thick, uniform piece. This helps it roast evenly. See pictures in the post above to get an idea.
Tie the lamb with butcher’s twine. I keep it simple by sliding 5 to 6 pieces of twine underneath, and then knotting them firmly on top. Trim the excess twine from each knot.
Rinse your basmati rice 2 to 4 times and soak it before you put the lamb in the oven. By the time the pan juices are ready, the rice will be perfect for cooking in the oven.
Preheat your oven to 425F(220C). Set a baking rack over a 9 by 13 inch pan and lightly oil the rack. Place the lamb on top. Pour 1.5 cup of warm water into the pan making sure it doesn’t touch the meat. This creates gentle steam and keeps the lamb moist while it roasts.
Roast the lamb at 425°F (220°C) for 15 to 20 minutes to brown the outside and seal in the juices. Lower the oven temperature to 375°F (190°C), tent the lamb with aluminium foil and roast for another 40 to 50 minutes. Start checking the internal temperature around the 35 minute mark. A general rule is 15 to 20 minutes per pound. My 3 pound lamb leg took close to 50-55 minutes.
Use a meat thermometer for accuracy. For medium well, pull the lamb at 145°F to 150°F in the thickest part. Let it rest, still tented, for 15 to 20 minutes so the juices redistribute. The temperature will rise to about 155°F to 160°F during resting.
Once roasted, remove the rack from the baking pan on to a plate or board and cover the lamb with foil to rest.
While it rests, prepare the rice. Pour the juices collected at the bottom of the pan into a measuring cup. If there’s too much fat on top, gently spoon it off and discard it, otherwise the rice will turn oily and heavy. For soaked basmati rice, you’ll need twice as much liquid as rice, so top up the broth with water if needed.
Add 1 cup of well-soaked rice to the baking pan. Pour in 2 cups of the broth and add about ½ teaspoon of salt. Give it a gentle stir. Cover the pan tightly with foil.
Return the pan to a 375°F oven and bake for 18 to 22 minutes, until the rice is tender and the liquid is fully absorbed. Once done, leave the pan covered for another 4 to 5 minutes so the rice can firm up. This keeps the grains from breaking.
Fluff the rice and slice the lamb roast. Serve with green chutney and raita.