Melt the butter in a large saucepan over medium heat. Add the onions and garlic to the pan and saute until soft and translucent, 3 to 4 minutes. Add the flour and cook, stirring with a wooden spoon, to make a light roux, about 2 minutes. Whisking constantly, slowly add the milk and continue to cook, stirring occasionally until thickened, 5 minutes. Add the salt, pepper, nutmeg, spinach and 1 1/2 cups of the Parmesan and cook, stirring, until thickened, about 2 minutes.
Remove from the heat. Place a piece of plastic wrap directly on the surface of the creamy sauce until ready to assemble the lasagna.
Set a large, 12-inch saute pan over medium heat and add the olive oil. Brown the sausage until golden brown and cooked through, about 4 to 5 minutes. Stir in artichokes. Transfer to a plate to cool and set aside.
Preheat the oven to 375 degrees F.
Coat a 9-by-13 inch baking dish with olive oil, and spread about 1/2 cup of the bechamel sauce on the bottom of the dish. Lay 3 sheets of pasta across the bottom of the dish and spread 3/4 cup of the bechamel sauce over the pasta. Sprinkle 1/4 of the chicken and artichoke mixture over the bechamel sauce, then sprinkle with 1/4 cup of the remaining Parmesan. Lay another 3 sheets of pasta over the chicken and artichokes. Repeat 2 additional times with the remaining bechamel sauce, chicken and artichokes, Parmesan, and pasta, ending with a layer of pasta covered with bechamel sauce. Sprinkle the remaining 1/2 cup of Parmesan over the bechamel sauce and scatter the butter pieces over the top. Place the casserole on a lined baking sheet and bake, uncovered, until bubbly and beginning to brown, about 45 minutes.
Remove from the oven and cool for at least 20 minutes before serving.
Sponsor recipe courtesy of Kelsey Nixon for Lipton