Start by burning one of the aubergines on a gas hob. Line the area around the hob head with foil, and put the aubergine directly on to a moderate flame and roast for 12-15 minutes, turning frequently with metal tongs until the flesh is soft and smoky and the skin is burnt all over. Keep an eye on them the whole time so they don't catch fire. The aubergine needs to deflate completely and the skin should burn and break.
Remove from the heat and make a long cut through the aubergine. Scoop out the soft flesh while avoiding the skin. Discard the skin, roughly chop the flesh then set aside.
Cut the other aubergine into 1.5cm dice. Heat 80ml of the olive oil in a frying pan and fry the aubergine dice in batches until golden and crisp. Transfer to a colander and sprinkle with salt. Leave to cool.
To make the risotto, put the onion and rest of the oil in a heavy-based pan and fry slowly until soft and translucent. Add the garlic and cook for 3 more minutes. Turn up the heat and add the rice, stirring to coat it in the oil. Fry for 2-3 minutes. Add the wine (it should hiss) and cook for 2-3 minutes, or until nearly evaporated. Reduce the heat to medium.
Now start adding the hot stock to the rice, a ladle at a time, waiting until each addition has been fully absorbed before adding the next, stirring all the time. When all the stock has been added, remove the pan from the heat. Add half the lemon zest, the lemon juice, chopped aubergine flesh, butter, most of the parmesan and ¾ tsp salt. Stir well, then cover and leave aside for 5 minutes. Taste and add more salt if you like, plus some black pepper.
To serve, spoon the risotto into shallow bowls and sprinkle with the diced aubergine, the remaining parmesan, the basil and the rest of the lemon zest.