Butter: Place the butter into the bowl. Melt at 100 degrees Celsius for 2 minutes on Speed 1.
Sprinkle the flour on top and cook at 100 degrees Celsius for 1 minute on Speed 1.
Cook bechamel: Add milk, salt, and nutmeg. Blitz shortly on Speed 5. Cook at 100 degrees Celsius for 8 minutes on Speed 2. Adjust the taste.
In the meantime preheat the oven to 200 degrees Celsius/ 400 degrees Fahrenheit.
Assemble the lasagna
Lightly butter a baking dish of about 31x20 cm/ 12x8 inches.
Scoop a few tablespoons of the meat sauce into the dish, just enough to have a thin layer.
Layer lasagna: Cover with noodle sheets. I needed 3 to form a layer. Cover with ⅓ of the meat sauce. Sprinkle some of the grated cheese on top. Cover with ⅓ of the bechamel sauce and sprinkle with a little more of the cheese.
Repeat: noodle sheets (3) + ⅓ of the meat sauce + sprinkle of cheese + ⅓ of the bechamel + sprinkle of cheese.
Repeat: noodle sheets (3) + ⅓ of the meat sauce + sprinkle of cheese + ⅓ of the bechamel + all the remaining cheese.
Bake for 30 minutes or until the cheese is bubbly, golden, and melted and the noodles are cooked through. Check the noodles by poking them with a fork, they should be soft.
Rest for 10 minutes before cutting into squares and serving.