1. To make the sauce: Heat the extra-virgin olive oil in a large saucepan over medium heat. Add the onion and cook and stir until translucent, 5 to 7 minutes.
2. Add the tomatoes, basil, and salt, and reduce the heat to low. Cook for 15 minutes, stirring occasionally with a wooden spoon. Remove from the heat and set aside. (This sauce does not require much cooking because it will be baked in the oven.)
3. To make the Parmigiana: In a large mixing bowl, combine the lour and 1¼ cups (150 g) of Parmigiano-Reggiano cheese with the garlic, mint, salt, eggs, and water. Whisk until you have a smooth batter. Set aside.
4. Peel the eggplant and slice them lengthwise, ¼ inch (6 mm) thick. You may also use a mandoline for greater precision. You will need about 20 large slices from the center of the eggplant. Use any of the smaller pieces to patch holes at the end if necessary.
5. Heat the frying oil, about 1½ inches (4 cm), in a large heavy-bottomed skillet over medium-high heat.
6. Dip the eggplant into the batter, allow the excess to drip off for a few seconds, and fry in batches until golden brown, 2 to 3 minutes per batch. Transfer to a paper towel–lined plate to drain.
7. Preheat the oven to 400F (200C).
8. Spread about 1 cup (255 g) of the sauce on the bottom of a high-sided 11 × 8-inch (28 × 20 cm) baking pan.
9. Place a layer of the eggplant slices over the sauce. You should need about 4 slices per layer. Cut the pieces to fit the pan if necessary. Spoon another light layer of tomato sauce over each of the eggplant slices. Add about one-quarter of the shredded mozzarella and top with 2 tablespoons (16 g) of Parmigiano-Reggiano. Cover the cheese with a layer of 4 slices of mortadella.
10. Next, place another layer of eggplant slices. Spread another light layer of sauce and top with one-quarter of the mozzarella and 2 tablespoons (16 g) of Parmigiano-Reggiano. Add 4 mortadella slices. Repeat the process of layering the eggplant, sauce, cheeses, and mortadella once more.
11. Add one final layer of eggplant. Patch up any holes with either cut pieces of the eggplant or smaller pieces. Spread the rest of the sauce over the eggplant and sprinkle with the remaining 2 tablespoons (16 g) of Parmigiano-Reggiano.
12. Bake uncovered for 30 minutes. Sprinkle with the remaining quarter of mozzarella. Bake for 10 more minutes, until the sauce and cheese are bubbling.
13. Remove from the oven and let rest for 10 to 15 minutes before cutting.
Nonna Romana Says
Don’t oversauce the Parmigiana or it will fall apart when you try to cut it. I love cutting into it and being able to see all of the beautiful, defined layers, but if you prefer more sauce, make a little extra sauce and serve it on top.
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