Begin by making the salt crust. This can be done the day before if desired. Combine all the ingredients in a mixing bowl and knead for approx. 5 minutes. Cover and allow the dough to rest for at least 15 minutes.
Divide the dough in two, making one piece slightly bigger, then roll out the two doughs approx. 5mm thick into an oval shape for the sweet potato to sit it.
Preheat an oven to 180°C.
Lay the sweet potato in the middle of the small piece then drape the large piece of dough over the potato, pressing all around the potato to remove air and secure the dough together. Trim excess dough and use a fork to press all the way around the outside. Carefully transfer to a baking tray and cook for approx. 1.5 hours.
Toss the nuts and pepita seeds in the olive oil, ground cumin and smoked paprika and roast in the oven. After 5 minutes, remove and cool.
Place the rice and saffron in a small saucepan. Cover with 3 cups of water and a pinch of salt. Bring to the boil, turn down, cover and cook on a low heat for 10 minutes. Remove from the heat and let sit for 10 minutes before removing the lid and spooning the rice into a mixing bowl to cool slightly.
Meanwhile, place the slice onions and oil in a small saucepan. Season and cook over a low heat for 20 minutes until soft and beginning to caramelize. Set aside.
Combine the rice with the nuts, seeds, sultanas, onions, carrot, pomegranate and coriander. Season and mix well. Place into a serving bowl.
Combine the yoghurt with the sumac, cumin, garlic, lemon juice and season. Spoon into a serving bowl.
Check the Sweet potato is ready by inserting a skewer through the crust and into the potato. It should go in easily. Once ready. serve using a small sharp knife to cut the crust around the sweet potato and remove the lid. Slice the sweet potato and serve with the rice and yoghurt.