1 Cut or tear the mozzarella into pieces and drain in a sieve for 1 hour, or up to overnight in the fridge.
2 Preheat the oven to 220℃ / 200℃ fan / gas mark 7.
3 Grease a baking tray with a little oil.
4 Lay the aubergine slices onto the prepared tray. Brush with oil and season lightly with salt and pepper. Roast the aubergines for 25–30 minutes, or until lightly browned. Remove from the oven and leave to cool briefly.
5 To create the tomato sauce, finely chop the onions and add to a frying pan with all other ingredients
6 Use a potato masher to brake up the tomatoes. Bring the sauce to the boil and then lower heat allowing it to bubble rapidly
7 Cook for 9 minutes until onions are softened
8 Puree the sauce until smooth
9 Match together similar-sized aubergine circles - three for each tower.
10 Spoon 1 heaped dessert spoon of tomato sauce onto one circle. Top with a basil leaf and a little of each cheese. Add another aubergine circle and repeat with the sauce, leaf and cheese. Top with the final aubergine circle followed by the sauce, leaf and cheese.
11 Repeat for the remaining towers, place in an ovenproof dish and bake for about 45 minutes or until cheese is lightly browned.