Heat 2 tablespoons of the oil in a frying pan over a medium-high heat. Quarter and add the aubergines and fry for 6 to 8 minutes, or until tender, tossing well to colour them all over. Set aside. Peel and finely grate the ginger and garlic, then peel and very finely slice the white onion (use a mandolin if you have one). Add the rest of the oil to the pan, tip in the cumin and mustard seeds and fry until they begin to pop. Lower the heat slightly, add the curry leaves and dried chillies and continue to cook until the leaves are crisp and translucent. Stir in the ginger and garlic and fry for 1 minute. Add the sliced onion along with ½ teaspoon of sea salt, lower the heat and cook for 5 to 7 minutes, or until the onion is soft. Stir in the tomato purée, garam masala and coconut milk. Bring it to a simmer, return the aubergine to the pan and cook for 10 minutes, or until it’s soft but still firm to the bite. Finely slice the red onion, pick and chop the coriander leaves, then combine in a small serving dish. Divide the curry between bowls and serve with the red onion salad and poppadoms, if you like.