I roast a leg of lamb about twice a year. Almost invariably, one of those times is Easter. I like it because it is large enough to feed a crowd and, if it is butter­flied, it does not take that long to grill (either over coals outside, or under the grill element of an oven), leaving plenty of time to prepare side dishes and dessert.

Indian spice and yogurt-marinated leg of lamb

Have the butcher butterfly the leg of lamb, rather than just removing the bone. When it is butterflied, the lamb is more even in thickness. As always with a large cut of meat, I strongly advise using a meat thermometer, preferably a battery-operated probe type, that will beep when the meat reaches the correct temperature.

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The spice mix is adapted from a version by one of my favourite food writers, J. Kenji López-Alt, from the website Serious Eats, who uses it for tandoori game hens. His spice mixture makes enough for two legs of lamb but it is worth making the entire amount, rather than halving the recipe; store the excess in an airtight container and freeze it for another occasion.

If you are making this for dinner tonight, the first thing to do is to rush out this morning and buy your butterflied leg of lamb and any other ingredients you might need. As soon as you get home, sprinkle the lamb with salt and let it sit at room temperature for at least an hour. This gives you plenty of time to make the spice mix, and several hours to marinate the lamb before it’s time to cook dinner.

1 butterflied leg of lamb, about 2kg
Fine sea salt, for sprinkling

For the spice mixture:
12 grams whole cumin seeds
5 grams whole coriander seeds
20 grams smoked paprika
4 grams ground turmeric
1 gram ground cayenne
12 grams achiote/annatto seeds
8 garlic cloves
A 10cm chunk of fresh ginger, peeled and roughly chopped
50 grams fine sea salt
60ml fresh lemon juice
250 grams whole milk Greek yogurt

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Lay the leg of lamb on the work surface and sprinkle both sides liberally with salt. Leave at room temperature for at least an hour.

Put the cumin seeds into an unoiled skillet and toast over a medium flame until fragrant, stirring almost constantly. Transfer the cumin seeds to the bowl of a small grinder (preferably a high-speed grinder, such as a Nutribullet). Put the coriander seeds into the same skillet (no need to wash it) and toast them the same way, then add them to the cumin seeds, along with the paprika, turmeric, cayenne and achiote/annatto seeds. Process until the spices are finely ground. Add the garlic cloves, ginger and salt, then grind again.

Divide the mixture into two even portions, putting half into a medium-sized bowl, and the remainder into an airtight container (freeze until needed). Mix the lemon juice and yogurt into the spice mixture, then rub this over the entire surface of the lamb. Fold or roll the lamb so you can put it in a container that fits in your fridge. Refrigerate for several hours, or until two hours before it is time for dinner.

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Take the lamb from the fridge an hour before you want to start cooking it. Scrape off most of the marinade. If cooking indoors, lay it fat side down on a lightly oiled tray large enough to hold the lamb flat. Preheat the oven’s grill to high. When the grill is hot, slide the tray into the oven so the meat is about 3cm from the heat element. Cook until the heat-exposed side of the lamb is sizzling and browned in spots.

Take the tray from the oven and flip the meat over so the fat side is up. Insert a probe-type meat thermometer into the thickest part of the lamb and set it to go off at 50 degrees Celsius (if you want it medium-rare). Slide the tray back into the oven so the meat is about 5cm away from the heat source. Cook the lamb, watching it carefully so it does not burn; if it starts to brown too much, move the tray further from the heat. Cook until the thermometer reaches 50 degrees, then take the tray from the oven and leave to rest for about 15 minutes; the internal temperature will continue to rise to about 60 degrees, which is what you want for medium-rare lamb.

If cooking the lamb over coal, start preparing the grill at least 30 minutes before you want to cook, if using a chimney starter, or longer using other methods. When the coals are hot, arrange them around the perimeter of the grill and place the rack about 10cm above the heat. Scrape the marinade from the lamb.

Place the lamb fat side up on the grill and cook uncovered for about 10 minutes, or until the meat is nicely charred in spots. Flip over the lamb, then insert the meat thermometer into the thickest part, setting it to go off at 50 degrees. Cook the meat over the coals, watching it carefully so it does not char too much; if it gets too dark, move the rack higher above the coals. When the thermometer goes off, let the meat rest for about 15 minutes.

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For both cooking methods, slice the lamb against the grain and serve with roasted potatoes, naan bread, a variety of chutneys and whatever other side dishes you like.

When ready to use the excess spice mixture, thaw it in the fridge. Mix it with 60ml of lemon juice and 250 grams of yogurt before spreading it over lamb or chicken.