Grind the saffron threads to a powder with a mortar and pestle, transfer to a small bowl and pour over 2 tablespoons of hot water. Set aside. Peel and finely dice the onion.
In a large frying pan, cook the onion in 2 tablespoons of oil over a low heat. After 10 minutes, add the tomato purée, cinnamon, turmeric, cumin, 1 teaspoon of sea salt, ½ teaspoon of freshly ground pepper, chopped tomatoes and split peas.
Pour in about 500ml of water and simmer everything over a low heat for 45 minutes or until the split peas are soft.
Spear the dried limes on a metal skewer, then add to the pan and cook, covered, for another 15 minutes. Once the cooking time is up, add the saffron water and stir through thoroughly. Remove the skewer from the limes.
Meanwhile, halve one large aubergine lengthways, then slice each half again lengthways into three equal spears. Salt generously and then let sit for 30 minutes. Pat dry.
Heat some oil in a small pan to a depth of 2cm. Fry the aubergine over a medium heat in batches of 2 or 3 spears, until golden brown. Drain on kitchen paper.
In a small pan over a medium heat, melt the butter and gently fry the barberries until softened.
To serve, place one fried aubergine spear on top of each portion of yellow split peas, with the rice on the side and barberries scattered on top.
Dried limes and barberries are often used in Persian cooking. Find them in Middle Eastern spice shops or buy online at souschef.co.uk.