Start by slicing the eggplant lengthwise into thin (5mm) slices.
If deep-frying the eggplant: Place the slices onto a large plate or into a sieve, one next to another. Sprinkle with some coarse salt. Create another layer and sprinkle again with salt. Continue with layers and salt until all the slices have been placed. Then place another plate on the eggplant slices with sufficient weight to get rid of excess water from the slices. Wait for 30 minutes - 1 hour. Rinse away the salt and set aside.
In the meantime, in a saucepan, add some olive oil and finely diced onion. Cook for a few minutes. Add the tomato passata, a few spoonfuls of water, some pepper, and salt. Cook for 40 minutes over low heat. Add basil leaves when 5 minutes are left of cooking time. (Leave some basil for garnishing the dish.)
In the meanwhile, cut the mozzarella into cubes and let it lose its excess moisture in a sieve.
If deep-frying the eggplant: For crispier slices, coat them in flour first. Fry some slices per time for 2-3 minutes in hot oil (about 170°C/340°F). Dry with paper towels.
If baking: Brush each slice with some olive oil, and bake for 20-25 minutes in a preheated oven (220°C/430°F) until lightly brown.
When the sauce is ready, preheat the oven to 200°C/400°F. Spread some sauce onto the bottom of a 20x30cm baking dish.
Top with a layer 1/3 of the eggplant slices. Spread 1/3 of the remaining tomato sauce on top. Add 1/3 of the mozzarella cubes, and 1/3 of the Parmesan cheese.
Create the second and third layer in the same way.
Bake for 35-40 minutes. Before serving, let rest for a few minutes and, finally, add fresh basil leaves to garnish.
Caution
Nutritional information shall not be used for medical reasons.
Keyword authentic eggplant italian dish, eggplant parmigiana