Cook the lasagna noodles in salted water until they reach al dente (follow the package instructions to cook). Drain and set aside.
In a 4 quart saucepan, melt butter over medium heat. Add the flour, pepper, salt, garlic powder, and onion powder to the melted butter and cook for 1-2 minutes until mixture is browned and bubbly.
Whisk the mixture while slowly pouring in milk until smooth and combined. Continue cooking over medium heat until mixture reaches a low boil and begins to thicken (6-8 minutes).
Add cream cheese and ½ cup shredded jack cheese to the white sauce. Stir, still cooking over medium heat, until cheese is melted and sauce is thoroughly combined. Remove from heat.
Stir the spinach leaves into the white sauce and set aside.
In a small mixing bowl, combine ricotta cheese, egg, parsley, and another ½ cup of jack cheese.
In a greased 9”x13” glass baking dish, spoon a bit of the sauce to cover the bottom of the pan. Place three lasagna noodles side by side into the pan. Spread ½ of the ricotta mixture over the noodles and top with ½ of the chicken. Spoon ⅓ of the sauce over the chicken and ricotta and top with 1 cup each of mozzarella and jack cheese.
Place another layer of noodles, the remaining ricotta, the remaining chicken, and another cup of both mozzarella and jack cheese.
Top with the remaining noodles, the remaining sauce, and finally, with the remaining cheeses.
Bake lasagna for 30-35 minutes or until sauce is bubbling up and cheese is melted and beginning to brown.
Remove from oven and garnish with fresh parsley, if desired.
Notes
The roux (which is cooking the flour and butter together) adds flavor and thickens the milk to make the white sauce. It’ll also provide a good base for the cheese to melt so that you don’t end up with a stringy gloppy texture and appearance.
Since the heat from the cream sauce softens the spinach, there’s no need to further cook the spinach. In fact, overcooked spinach can develop a chalky taste which is the last thing you want. While 4-5 cups of spinach may seem like a lot, it does wilt down substantially.
You do have the option of adding onions and garlic to the roux instead of the powder form. I prefer the powder form since it’s quick and easy, especially since there’s quite a bit to be done before the lasagna bakes. If you opt to use raw ingredients instead, sauté the onion (1 cup diced small) and garlic (2-3 cloves, minced) in the butter before adding the flour, salt, and pepper.
You can use a different cheese like parmesan or add parmesan as an additional cheese for extra flavor.