Who better to perfect a classic Italian baked eggplant Parmesan casserole than the Northern Italian twin chefs Nicola + Fabrizio Carro.
Heat olive oil in a large pot over medium heat. Add onions and cook, stirring until soft and translucent, 10 to 15 minutes. Add tomatoes and reduce heat to low. Cook, stirring occasionally and taking care not to let sauce stick to the bottom of the pot, about 2½ hours. Remove from heat and, using an immersion blender, blend until smooth, adding basil leaves as you blend.
Alternatively, working in batches, you can transfer tomato sauce to the jar of a conventional blender, adding basil leaves as you blend. Season with salt and pepper and reheat to use immediately or let cool completely before transferring to an airtight container. Refrigerate until ready to use, 3 to 5 days.
Lay eggplant slices in a single even layer on a rack set over rimmed baking sheets; generously season with salt. Let stand 15 minutes to release excess moisture; pat dry with paper towels. Place flour in a shallow dish; dredge eggplant slices in flour, shaking off excess. In a large pot, heat canola oil to 300° on a deep-fry thermometer.
Working in batches, add eggplant slices to hot oil and cook, turning once, until lightly browned, about 3 minutes per side.Transfer to a paper towel-lined baking sheet to drain; repeat process with remaining eggplant.
Place mozzarella and Grana Padano cheeses in the bowl of a food processor; process until just combined. Add basil leaves and olive oil; process until well combined. Season with fine sea salt and pepper.
Preheat oven to 350 degrees. Set ring molds in a large shallow baking dish. Place a dollop of tomato sauce at the bottom of each ring mold. Top with a slice of eggplant. Spoon an even layer of cheese mixture on top of eggplant.Top with another dollop of sauce, followed by another slice of eggplant. Repeat process until you have reached the top of the ring mold or have created four layers, ending with a slice of eggplant. Top with a little tomato sauce.
Transfer to oven and bake until cheese is melted and eggplant is warmed through, about 15 minutes. Using a spatula, carefully transfer filled ring molds to individual serving plates. Carefully remove ring mold before serving.