Slideshow: More Amazing Lamb Recipes
Melt the butter in a medium saucepan. Stir in the flour until a paste forms. Remove the pan from the heat and whisk in the cream. Set the saucepan over moderately high heat and whisk in the milk. Whisk constantly until the sauce starts to boil. Reduce the heat to moderate and whisk occasionally.
Add the half-onion, bay leaf and cloves to the sauce and simmer over moderately low heat, whisking often, for 12 minutes. Remove from the heat, whisking occasionally until just warm. Strain into a bowl and whisk in the yogurt. Season with nutmeg, salt and pepper. Lay plastic wrap directly on the sauce.
Preheat the oven to 500°. Soak the currants in warm water. Set a colander over a large bowl.
In a large, deep skillet, heat 2 tablespoons of the oil. Add the beef and lamb and cook over moderately high heat, breaking up the meat, until it begins to brown, 5 minutes. Stir in 1/2 tablespoon of the ras el hanout, 1/2 teaspoon of the cinnamon and 1/2 teaspoon of red pepper. Season with salt and pepper and scrape it into the colander to drain.
Heat 2 tablespoons of the oil in the skillet. Add the garlic and diced onions and cook over moderate heat, stirring occasionally, until softened, about 6 minutes. Add the remaining 3 tablespoons of ras el hanout, 2 tablespoons of cinnamon and 1/2 teaspoon of red pepper and stir until fragrant, 2 minutes. Add the wine and boil until reduced to 2 tablespoons, 6 minutes. Add the tomatoes, their juices and the meat; simmer over moderate heat for 5 minutes. Drain the currants and stir them in; simmer for 5 minutes. Season with salt and pepper.
Arrange the eggplant slices on 2 large, rimmed baking sheets. Brush both sides of the eggplant with olive oil, season with salt and pepper and bake on the upper and lower racks of the oven for 10 minutes, or until tender. Preheat the broiler. Broil the eggplant, one sheet at a time, for 1 minute, or until lightly charred. Reduce the oven temperature to 350°.
In a medium skillet, heat the remaining 2 tablespoons of oil. Add the diced bell peppers and cook over moderate heat, stirring occasionally, until softened, about 7 minutes.
Arrange the eggplant in a 10-by-17-by-2-inch oval baking dish. Spread the bell peppers and meat filling over the eggplant. Spread the béchamel sauce over the meat and sprinkle the cheese on top. Bake the moussaka for 30 minutes, or until bubbling. Preheat the broiler. Broil the moussaka in the center of the oven for 2 minutes, or until browned. Let rest for 10 minutes then serve.
Ras el hanout, a Moroccan spice blend, is available at specialty and Middle Eastern markets.