Cook the lasagna noodles according to package instructions. Drain and set aside.
In a saucepan over medium heat, melt butter. Add flour and stir continuously to form a roux.
Gradually whisk in milk until the mixture thickens into a smooth white sauce. Season with salt, pepper, and nutmeg.
In a bowl, mix ricotta cheese, minced garlic, and spinach. Add salt and pepper to taste.
Preheat oven to 375°F (190°C).
Spread a layer of white sauce in a baking dish. Add a layer of noodles, then ricotta mixture, followed by mozzarella cheese.
Repeat layers until all ingredients are used, finishing with sauce and mozzarella on top.
Cover with foil and bake for 30 minutes. Remove foil and bake for another 15 minutes until golden and bubbly.
Let the Creamy White Lasagna rest for 10–15 minutes before slicing and serving.