1. To make meat sauce, melt butter in a large skillet; add onion; sauté until golden. Add beef and lamb; sauté until browned. Add the garlic, tomato sauce, salt, bay leaf, oregano, and cinnamon; heat to simmering. Cover and cook over low heat, stirring occasionally, 30 minutes. Stir in the parsley.

2. While meat sauce is cooking, prepare the béchamel sauce. Melt the butter in a saucepan; gradually stir in the flour until a smooth paste forms. Sauté, stirring constantly, over low heat 3 minutes. Gradually stir in the milk; whisk over medium heat until sauce is thickened and smooth and comes to a boil. Beat the eggs thoroughly in a large bowl; gradually add the hot sauce to the eggs, whisking thoroughly. Add the salt, black pepper, and nutmeg.

3. Cook the elbow macaroni in plenty of boiling salted water until slightly undercooked, about 10 minutes; dram.

4. Heat oven to 350°F. Select a 3-quart or 14 × 10-inch baking dish. Generously butter dish. Add half the cooked macaroni. Sprinkle with half the cheese. Top with all of the meat sauce. Spoon remaining macaroni over sauce. Pour béchamel sauce over top and sprinkle with remaining cheese.

5. Bake until custard is set and top is browned and bubbly, about 50 minutes. Let stand about 15 minutes before cutting into squares and serving.