Boil all the lasagna sheets, 2 at a time, for 2-3 minutes in very salted water and place in bowl with ice water until ready to assemble.
Make 1 L béchamel: warm milk gently in a pot. Cook roux until butter smells toasted. Remove roux pot from heat. Add a ladle of gently warmed milk to roux and whisk. Repeat. Then add remaining milk while whisking. Return pot over medium heat and stir constantly until it’s like a medium custard consistency. Add salt, pepper, nutmeg to taste. Whisk in cheese.
Layer lasagna in a deep 9x13 baking dish or roaster: Add 2 scant ladles of bolognese on bottom of pan with a generous amount of the oil. Add noodles on top, slightly overlapping in the middle. Add 2-3 ladles of bolognese, not too thick as you will want to see some noodle through the sauce.
Add 2-3 ladles of the béchamel overtop in a snake-like pattern.
Top with a portion of cheese.
Continue layering until all noodles are used. For the finishing layer, use more bechamel and sprinkle generously the last batch of cheese. More cheese is better :)
Bake @ 350 until the lasagna is bubbling and golden on top (45-60 minutes). Let sit 10-15 minutes to allow it to set. It’s very rich, cut accordingly.