In a large saucepan, add 5 cups (1.25L) water and 2 tsp sea salt flakes. Bring to the boil. Add the rice and cook, stirring occasionally, for 10 mins or until rice is slightly al dente but not crunchy. Rinse under cold water and drain well.
In a medium bowl, combine 11/2 cups of the semi-cooked rice with yoghurt.
Heat a 25cm (base measurement)non-stick frying pan over medium heat. Melt butter with ¼ cup (60ml) oil. Add yoghurt mixture. Spread evenly with the back of a spoon to coat base of the pan. Top with remaining rice, creating a mound towards the centre. Use handle of a wooden spoon to create 5-6 holes in the rice down to the base of the pan.
Cook the rice, rotating the pan 90 degrees every 5 mins to ensure even browning underneath, for 20 mins. Reduce heat to low. Cover and cook for 15 mins or until edges are deep golden and the rice is tender. Uncover the pan, being careful not to allow condensation on lid to drip back onto the rice. Gently loosen rice from the side of the pan. Place a large round platter over the pan and carefully invert rice onto platter.
Meanwhile, using a small sharp knife, cut away the peel and white pith from the grapefruit. Working over a bowl to catch the juice, cut between membranes to release segments. Reserve 2 tbs juice in bowl. Coarsely chop segments and return to bowl with the reserved juice.
In a separate bowl, combine shallot, garlic, sugar, 1 tbs lemon juice and 1 tsp salt. Set aside for 10 mins to develop the flavours. Add grapefruit segments, grapefruit juice, lemon rind, coriander, chilli, if using, and 1 tbs oil. Season the chermoula with salt and pepper.
Heat a large non-stick frying pan over high heat. Coat the lamb with the remaining 1 tbs oil and season with salt and pepper. Cook for 3 mins each side for medium-rare or until cooked to your liking.
Transfer the lamb to a serving platter. Spoon chermoula over the lamb and serve with the crispy rice.
Tip: SERVE WITH lemon zest and coriander sprigs