Make Sauce: In a saucepan, melt butter over medium heat. Add garlic and cook 1 minute. Stir in flour and cook for another minute. Slowly whisk in milk, broth, and cream. Add salt, pepper, and nutmeg. Simmer until thickened.
Prep Filling: In a bowl, mix shredded chicken and spinach with a few tablespoons of the sauce.
Layer Lasagna: In a greased 9×13 pan, spread a little sauce. Layer 3 noodles, half the chicken-spinach mix, spoonfuls of ricotta, mozzarella, and sauce. Repeat layers. Finish with noodles, sauce, and sprinkle Parmesan on top.
Bake: Cover with foil and bake at 375°F (190°C) for 25 minutes. Uncover and bake 15 more minutes until golden and bubbly.
Rest & Serve: Let sit 10 minutes before slicing. Garnish with parsley if desired.
