01 - Preheat oven to 400°F. Line two baking sheets with parchment paper for easy cleanup.
02 - Arrange eggplant slices on prepared baking sheets. Brush both sides generously with olive oil and season with salt and pepper. Roast for 20 minutes, flipping halfway through, until softened and lightly golden. Remove from oven and reduce heat to 375°F.
03 - In a medium bowl, combine ricotta cheese, Parmesan cheese, egg, chopped basil, nutmeg, salt, and pepper. Mix thoroughly until smooth and well incorporated.
04 - Spread 1/2 cup marinara sauce evenly across the bottom of a 9x13-inch baking dish. Arrange half of the roasted eggplant slices over the sauce, slightly overlapping if necessary. Spread half of the ricotta mixture over the eggplant, then top with 1 cup marinara sauce and 1 cup mozzarella cheese.
05 - Repeat the layering process with remaining eggplant slices, ricotta mixture, marinara sauce, and mozzarella cheese. Sprinkle the top evenly with the remaining 2 tablespoons grated Parmesan.
06 - Cover the baking dish tightly with aluminum foil. Bake for 25 minutes at 375°F to heat through and meld flavors.
07 - Remove foil and continue baking for 15-20 minutes until the cheese is bubbly and golden brown on top.
08 - Let the casserole rest for 10 minutes before serving to allow layers to set. Garnish with fresh basil leaves if desired.