Let’s dive into the cooking process. I promise it’s simpler than it seems, and the aroma filling your kitchen will be worth every step!

1. Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper.
2. Arrange the eggplant slices in a single layer on the prepared baking sheet. Drizzle with olive oil and season with salt and pepper. Roast for 20 minutes, flipping halfway through, until golden and tender.
3. In a large skillet over medium heat, heat the remaining olive oil. Add the onion and garlic, sautéing until softened and fragrant, about 3 minutes.
4. Add the ground beef or lamb to the skillet, cooking until browned. Stir in the crushed tomatoes, tomato paste, cinnamon, oregano, salt, and pepper. Simmer for 20 minutes, allowing the flavors to meld.
5. While the meat sauce simmers, prepare the béchamel. In a saucepan, melt the butter over medium heat. Stir in the flour, cooking for 1-2 minutes until a paste forms.
6. Gradually whisk in the milk, ensuring there are no lumps. Cook, stirring constantly, until the sauce thickens. Season with nutmeg, salt, and pepper. Remove from heat and let it cool slightly before whisking in the egg yolk.
7. To assemble the moussaka, reduce the oven temperature to 350°F (175°C). In a large baking dish, layer half of the roasted eggplant, all of the meat sauce, and half of the Parmesan cheese.
8. Add the remaining eggplant slices, pour the béchamel sauce over the top, and sprinkle with the remaining Parmesan cheese.
9. Bake for 45 minutes until the top is golden and bubbling. Allow it to rest for 15 minutes before serving, letting the layers set beautifully.