Preheat oven to 375°F (190°C). Grease a 9×13-inch baking dish with olive oil or cooking spray.

In a large skillet, heat olive oil over medium heat. Add chopped onion and sauté for 3–4 minutes until softened. Stir in minced garlic and cook for 1 minute until fragrant.

Add ground beef (or plant-based substitute) to the skillet, breaking it apart with a wooden spoon. Season with paprika, salt, and black pepper. Cook until browned and fully cooked through, about 8–10 minutes. Remove from heat and set aside.

Peel and thinly slice the potatoes, aiming for slices about ⅛-inch thick. Layer half of the potato slices evenly across the bottom of the prepared baking dish. Sprinkle lightly with salt.

Spread the cooked meat mixture evenly over the potatoes. Top with the remaining potato slices, arranging them in a single layer. Season with additional salt and black pepper if desired.

In a mixing bowl, whisk together eggs, yogurt (or sour cream), milk, and optional ground nutmeg or garlic powder until smooth. Pour the custard evenly over the layers.

Bake uncovered for 45–55 minutes, or until the top is golden and the potatoes are tender when pierced with a fork. The edges should be crispy, while the center remains creamy.

Remove the moussaka from the oven and let it rest for 10–15 minutes before slicing. Garnish with fresh parsley if desired, and serve warm.