Step 1

Heat the oil in a large pan over medium heat. Add the onions and cook until soft, stirring often, about 8 minutes. Add the pepper flakes, garlic, herbes de provence and 1 1/2 teaspoons of the four-spice powder. Add the lamb, raise the heat to medium high and let cook, breaking up any chunks, until browned, 5 to 8 minutes. Add the wine and simmer until reduced slightly. Add the tomatoes and season with salt and pepper. Lower the heat, cover and simmer until thick, about 45 minutes.

Step 2

To make the bechamel sauce, bring the milk to a simmer in a medium pot set over medium heat. Melt the butter in a medium saute pan over medium heat. Whisk the flour into the butter and cook for 2 minutes. Whisk the warm milk into the flour mixture. Add the remaining 2 pinches four-spice powder and cook for 5 minutes at a simmer, whisking often, until thickened. Remove from the heat.

Step 3

In a small bowl, whisk together the egg yolks. Whisking constantly, slowly pour a quarter of the milk mixture into the eggs. Whisk the egg mixture back into the pot. Whisk in 1 cup of the cheese. Fold in the yogurt. Season with salt and pepper.

Step 4

Preheat the oven to 375 degrees F.

Step 5

Bring a pot of salted water to a boil. Cook the pasta to al dente according to the package instructions. Drain and combine with the lamb sauce. Adjust the salt and pepper to taste.

Step 6

Transfer to a large baking dish and top with the bechamel sauce and the remaining 1 cup cheese. Bake until the top is caramelized, about 45 minutes. Garnish with the parsley.