Cook the pasta and rabe: Bring a large pot of well-salted water to a boil. Add pasta and five minutes before its cooking time is up, add the broccoli rabe. It will seem like too much for the water, but with a stir or two, the rabe should wilt and cook alongside the pasta. Drain the broccoli rabe and pasta together and place in a large bowl.

Cook your sausage: Meanwhile, heat 1 to 2 tablespoons olive oil in a large, wide saucepan over medium heat. When hot, add the sausage, breaking it up with a wooden spoon until it starts to brown, about five minutes. Remove with slotted spoon or spatula, leaving any fat behind.

Heat oven to 400 degrees.

Make the bechamel: Melt your butter in same saucepan over medium heat. Once melted, add your flour and stir it into the butter until smooth. Cook the mixture together for a minute, stirring constantly. Pour in a small drizzle of your milk, whisking constantly into the butter-flour mixture until smooth. Continue to drizzle a very small amount at a time, whisking constantly. Once you've added a little over half of your milk, you'll find that you have more of a thick sauce or batter, and you can start adding the milk in larger splashes, being sure to keep mixing. Once all of the milk is added, add the salt, garlic, nutmeg, and few grinds of black pepper, and bring the mixture to a lower simmer and cook it, stirring frequently, for 10 minutes. Taste and adjust seasonings if needed.

Assemble and bake: Add the sausage and bechamel to the bowl with the pasta and broccoli rabe. Stir in mozzarella and half of grated parmesan or pecorino until combined. Pour into a lasagna pan, deep 9×13-inch baking dish, or 3-quart casserole dish and coat with remaining parmesan or pecorino. Bake for 20 to 30 minutes, until the edges and craggy points are nicely bronzed.

Eat warm. Reheat as needed.