Wash the eggplant and cut off the stem.
Slice it lengthwise into thin slices. Salt the slices generously, place them in a colander, and let the salt draw out the moisture while the liquid drains into a bowl underneath. It’s a good idea to place something heavy on top to press out even more liquid. For example, cover the slices with a plate and place a 1 kg bag of flour on top. Let the eggplant drain for at least one hour.
Once the eggplant has released its moisture, rinse the slices thoroughly under plenty of water and pat them dry with paper towels or a kitchen towel. If they remain wet, they won’t grill properly.
Heat a grill pan over high heat. Drizzle in a little olive oil and grill the dried eggplant slices on both sides. Transfer them to a plate, or if you have already prepared the tomato sauce, you can place them directly into the baking dish.
Pour the tomato purée into a small saucepan. Season with salt, pepper, oregano, and basil, then simmer the ingredients together on the stove. Add one crushed garlic clove as well. Set aside.
Take a small ovenproof baking dish and drizzle in a little olive oil. Spoon in a few tablespoons of tomato sauce and spread it evenly. Layer some grilled eggplant slices over the sauce, then spoon more tomato sauce on top. Sprinkle with grated Parmesan cheese. Add another layer of eggplant slices, then cover with the remaining tomato sauce. Sprinkle with Parmesan again and top with sliced mozzarella.
Bake in a preheated oven at 200°C / 392°F for about 30 minutes.
Once removed from the oven, let it rest for at least 20 minutes before slicing and serving.