First, wash and trim the eggplants. Slice them lengthwise into long slices, about 1/4 inch (0.5 cm) thick if possible. Sprinkle the slices with a little salt and place them in a colander to drain. This helps remove some of the bitter liquid.

Meanwhile, finely chop the onion. Heat a little olive oil in a large skillet and sauté the onion for a few minutes until soft. Add the tomato sauce, salt, pepper, and a little water. Let it cook for 30–40 minutes.

As the title says, I didn't fry the eggplant—I quickly roasted them using the broiler (grill) setting at the top of the oven. Arrange the eggplant slices on an oiled baking sheet. Don't add more salt since you already salted them earlier. Broil for 4 minutes, then flip and broil for another 4 minutes. Repeat with all the slices. I used 3 baking sheets in total.

Once the eggplant is ready, your sauce should be done too. Adjust salt and pepper to taste and turn off the heat. Spread a little sauce on the bottom of your baking dish (I used an oval glass one), then layer the eggplant slices. Add a layer of diced mozzarella, grated Parmesan, and tomato sauce. For the next layer, arrange the eggplant slices in the opposite direction.

Add another layer of diced mozzarella, grated Parmesan, pepper, and finish with more sauce. For the final layer, top with sauce, the remaining mozzarella, and a generous sprinkle of Parmesan.