1. Melt butter in a saucepan over medium heat.

2. Whisk in an equal amount of all-purpose flour to create a roux, cooking for 2-3 minutes to remove the raw flour taste.

3. Gradually pour in warm milk, whisking constantly to prevent lumps from forming.

4. Bring the mixture to a simmer and cook, stirring frequently, until the sauce has thickened to a creamy consistency, about 10-15 minutes.

5. Season the béchamel with a pinch of nutmeg, salt, and pepper to taste.

6. Bring a large pot of salted water to a boil, then add the noodles and cook according to the package instructions, typically 8-12 minutes. Be sure to stir the noodles occasionally to prevent sticking. Once cooked, drain the noodles and rinse them with cool water to stop the cooking process.

7. Preheat your oven to 375°F (190°C) and lightly grease a 9×13 inch baking dish.

8. Start by spreading a thin layer of béchamel sauce on the bottom of the prepared baking dish.

9. Add a layer of cooked lasagna noodles, followed by more béchamel sauce, shredded chicken (if using), sautéed vegetables (if using), mozzarella cheese, and Parmesan cheese. Season with a pinch of garlic powder, salt, and pepper.

10. Repeat the layering process two more times, ending with a generous layer of béchamel sauce and cheeses on top.

11. Cover the baking dish with foil and bake for 25 minutes. Then, remove the foil and continue baking for an additional 10-15 minutes, or until the top is golden brown and the cheese is melted and bubbling.

12. Once the lasagna is done, let it rest for 10 minutes before slicing and serving.