Combine spinach, cottage and Parmesan cheeses, basil, and nutmeg in a large bowl. Sprinkle with salt and pepper. Mix in eggs.
Slice lasagna noodles in half crosswise. Spoon 2 tablespoons of cheese mixture onto each noodle half. Roll up. Arrange, seam side down in a cooking spray coated baking pan.
Stir together flour and milk in a small pot. Let boil, whisking continually until thick, about 1 minute. Take mixture off of heat and mix in margarine, salt, cayenne, and white pepper. Spoon sauce over noodles. Top with croutons.