Slice the aubergine lengthways into ½ cm pieces. Layer 3-4 pieces in the bottom of a colander and sprinkle generously with salt. Repeat with another few pieces of aubergines, sprinkling with salt and layering up the colander until all the aubergine pieces are salted.
Next, take a plate that’s a smaller diameter than the top of the colander and place it on top of the aubergine. Add a pestle and mortar or something heavy on top of the plate (e.g. kitchen weights, tinned cans). Place the whole colander contraption onto another plate to collect the juices and leave the aubergines to drain for at least 30 minutes, up to 3 hours.
Pat dry with kitchen towel or a clean tea towel, trying to remove as much of the liquid as possible.
While the aubergines are draining, make the tomato sauce. Warm 4 tablespoons of olive oil in a medium saucepan over a medium heat and add the onion. Season well with salt and leave to sauté, stirring well for about 10 minutes until it starts to soften and becomes translucent. Do not let it catch or burn. Add the garlic before adding the 2 tins of tomatoes, sugar and tomato paste. Reduce the heat to a medium and allow to bubble and simmer for about 30 minutes, stirring occasionally until the sauce has thickened.
Once the aubergines have drained their bitter juices, fry the slices in batches in a large frying pan over a medium-high heat in 1 cm of olive oil. Top up the oil as necessary and turn the aubergines every 3-4 minutes, allowing them to go completely golden and a little bit crispy on each side. Aubergines love olive oil so don’t be shy! You can pat off any excess afterwards if any pieces seem super oily to you.
Now preheat the oven to 180ºC/350ºF/gas mark 5 and assemble the parmigiana.
In a medium sized oven dish or roasting dish, add a thin layer of tomato sauce to the bottom. Next add a layer of aubergine slices to cover the bottom of the dish, tearing and pushing them if necessary to make a layer. Next add a ladleful of tomato sauce, perhaps a quarter to a third of the mix, spreading evenly over the top of the aubergines. Sprinkle some basil leaves on top of the tomato sauce and then add the next layer of aubergines.
Repeat until all the aubergines and tomato sauce have been used up. Finish with a generous sprinkle of a plant-based cheese – parmesan or mozzarella style work well. Alternatively, you could use breadcrumbs drizzled with olive oil for a golden crunchy topping. Finish with plenty of black pepper and a sprinkle of chilli flakes if you like. Bake in the pre-heated oven for 20-30 minutes until the parmigiana is golden on top and the aubergines are soft all the way through and juicy.
Leave to stand for at least 15 minutes before cutting, to give the sauce and layers a chance to firm up.
Serve with a crunchy green salad and bread to mop up the sauce. Enjoy!