TIP: If doubled, the ragu recipe freezes well. Rather than making it into lasagna the second-time around, defrost sauce, heat through then stir in 1 cup warm milk and simmer to thicken, serve with penne, rigatoni, pappardelle or bucatini as an alternative to classic Bolognese. Top with pecorino, mint and/or parsley.
For the ragu: Heat 2 tablespoons extra-virgin olive oil in a Dutch oven over medium-high heat. When the oil smokes, pat the ground lamb dry and add to pan, brown to caramelize the meat, season with rosemary, marjoram, cloves, salt, and pepper. Once the meat has browned, add the onion, carrot, garlic and cook to soften 10 minutes more, stirring frequently. Stir in tomato paste, cook 1 minute or until fragrant. Stir in stock then wine, reduce heat to low and gently simmer.
In salted boiling water, undercook the pasta by 2 minutes from package directions. Reserve a cup of starchy pasta liquid.
Meanwhile, heat the butter in a saucepot over medium heat, whisk in 2 tablespoons flour, 1 to 2 minutes, whisk in the milk and simmer to thicken. Season the bechamel sauce with salt, pepper, and nutmeg, to taste.
Drain the pasta and add back to the pasta pot. Toss the pasta with the lamb ragu and some of the reserved starchy cooking water to loosen. Pour the pasta into a large casserole. Scatter the spinach around on top of pasta.
Combine the ricotta with mint and/or parsley, dot the pasta with ricotta evenly around the casserole. Pour the bechamel sauce in even layer around the casserole and top with grated cheese. Cool and store for make-ahead meal. Reheat in 350 degree F oven, covered, for 30 minutes then raise the heat to 425 degrees F and bake uncovered, until brown and bubbly, 15 to 20 minutes.
To serve immediately, transfer the casserole to a preheated 425 degree F oven and bake about 15 to 20 minutes, to brown.