Sprinkle 1 tbsp curry powder into a bowl. Peel and finely chop or grate the garlic. Grate the zest from the lemon. Finely chop the coriander stalks (save the leaves for later). Stir all 3 ingredients into the bowl with the curry powder, along with half the yogurt and a good pinch of salt and pepper.
Completely unwrap the lamb and cut away the string. Unroll the meat and, using a sharp knife, make incisions lengthways into any thicker parts of the meat to even it out as much as possible. It should be about 5-6cm thick when finished. Pop the meat in a large roasting tin.
Pour the marinade over the lamb and rub well to make sure it is fully coated. Set aside for 30 mins to come to room temperature. From this point, continue using one of the following options.
Cooking indoors: Heat your oven to 200°C/Fan 180°C/Gas 6. Set a large, heavy frying pan on a high heat and add 1 tbsp olive oil.
When the pan is smoking hot, add the lamb. Fry for 2 mins on each side, till well coloured. Pop the lamb back in the roasting tin and slide into the oven. Cook for 25-30 mins for medium-rare, or another 10 mins for medium.
Set the cooked lamb to one side and let it rest for 20 mins before carving. Slice and serve on a platter with the remaining yogurt, the coriander leaves and wedges of the zested lemon.
Light your barbecue and bring to a medium-high temperature. Add the lamb and cook over the hot coals for 2 mins on each side, till well browned. Use tongs to transfer the meat to a cooler part of the grill and cover with a lid. Continue to cook, turning occasionally, for 25 mins for medium-rare, or another 10 mins for medium.
Set the cooked lamb to one side to rest for 20 mins before carving. Slice and serve on a platter with the remaining yogurt, the coriander leaves and wedges of lemon.
Know your grill:
When lighting your barbecue, lay the bulk of your coals to one side, gently sloping 3/4 of the way to the other side. This helps to regulate the heat, giving you fierce 'direct' heat to brown your meat over, and gently 'indirect' heat to slowly finish it off.
Prepare your lamb and slather with the tandoori yogurt marinade the night before cooking, to give all that flavour time to really seep into the meat.
Next week in the Summer Roast Box:
Sizzling Spanish Spatchcock Chicken. ORGANIC chicken rubbed with smoked paprika, fennel, garlic and herbs and grilled until smoky and crispy.
Guess what? Our new cookbook is launched soon! To celebrate this, our recipe writer Sam has packed our Super Salad box with two mighty fine recipes featured in the book. Both of which will sit very happily beside chunks of sizzling chicken.