Start by melting the butter in a pan over medium heat. Once it is bubbling, toss in the minced garlic, letting it cook until fragrant, about 1 minute. Be careful not to burn the garlic, as it will change the taste.
Whisk in the flour, cooking for a couple of minutes until it is lightly golden. Gradually add in the milk while continuously whisking for a smooth texture. If it clumps, just keep whisking!
Stir in the grated parmesan and softened cream cheese until melted and well mixed. Ensure there are no lumps from the cream cheese.
Fold in the baby spinach leaves and let them wilt in the sauce for a couple of minutes.
In a separate bowl, mix the cooked chicken pieces with ricotta and egg. Ensure the chicken is fully shredded for even distribution.
In a greased baking dish, start layering by spooning some of the sauce on the bottom. Smooth it out before adding the cooked lasagna noodles.
Continue layering with the chicken-ricotta mix, sauce, noodles, and finish with shredded mozzarella.
Place the completed dish into the oven and bake until bubbly and golden, around 45 minutes. Let it cool for about 15-20 minutes before slicing to hold its shape better while serving.