Heat a saucepan over a medium heat. Add 30g of the olive oil, add the onion and. Fry the onion for 4-5 minutes, or until softened. Add the garlic and continue to cook for one minute.
Pour in the tomatoes and mix well. Season with a salt, pepper and pinch of sugar. Reduce the heat and simmer for 20-30 minutes, or until the tomato sauce is thickened.
Meanwhile slice the aubergines into slices 1cm thick. Brush the aubergine slices with olive oil and season with salt and pepper. Place them on a baking tray with baking paper. Roast the aubergine slices in the oven at 170C until the are golden brown.
Place six aubergine slices on a baking. Pour one tea spoon of tomato sauce on top. Lay another six slices on top and a pour a spoon of tomato sauce. Repeat this another two time. All together you need to have four layers of aubergine slices. At the end put one thick mozzarella slice on each six aubergine towers.
Bake into preheated oven until the mozzarella melted and golden-brown on top.