Sauce: Heat the milk until very warm but do not bring to a boil.
In another pan over medium heat, melt the butter.
Do not let the butter brown.
Whisk in flour and cook for 3 or 4 minutes, stirring constantly.
Gradually add the hot milk.
Continue to whisk until the sauce is thickened.
add the freshly grated nutmeg if using.
Sauté the garlic and onions in the butter or oil until the onions are translucent.
Stir in the spinach and 1/2 cup of the parsley.
Add a little water if the spinach is dry.
Cook until the spinach wilts then remove it from the heat; set aside.
Mix the remaining parsley, ricotta, eggs and 2/3 of the parmesan cheese together.
You may cook the lasagna until al dente or don't cook them at all.
Moosewood does not cook theirs, they just layer the raw noodles in the pan.
Oil a large casserole or lasagna pan.
Layer the ingredients as follows: 1 1/2 to 2 cups of sauce, 1/3 of the noodles, 1/2 of the spinach, all the mozzarella, 1 1/2 to 2 cups sauce, 1/3 of the noodles, all the ricotta mixture left, all of the spinach left, 1 1/2 to 2 cups of the sauce,the remaining noodles, the rest of the sauce, sprinkling the remaining parmesan cheese on top.
Cover the casserole and bake at 350°F for 45 minutes.
Uncover the casserole and bake for another 10 to 15 minutes.
Remove the casserole from the oven and let it rest for 10 to 15 minutes before serving.