Preheat oven to 375.
Before you start rolling out the pasta dough, make sure that your bechamel and tomato sauce are cooked and cooled. Spread a layer of 2-3 tbsp of tomato sauce in the bottom of your loaf pan.
Divide the pasta dough into 12 equal pieces. Feed one piece through the pasta roller set on the thickest setting (usually #1). Fold the rolled dough into thirds and feed through a second time. Repeat this process, gradually working your way up to the thinnest setting (#7 or 8), until you have a thin, almost translucent sheet of dough.
Holding the dough sheet gently, place it in the loaf pan. Trim and remove any excess dough that comes up the sides. Top with a thin layer of bechamel followed by a thin layer of tomato sauce.
Repeat this process. Roll out each segment of dough to the thinnest setting on your pasta roller, transfer to the loaf pan and top with bechamel and tomato sauce. Don't roll out all the sheets of dough at once; they're too delicate to sit. Roll each one out as you layer.
For the final layer, top with bechamel, tomato sauce and a generous sprinkle of parmesan cheese. Bake until browned, about 45 minutes.
Set the lasagna aside to rest for at least 2 hours, but it can be kept in the fridge for up to 2 days.