Beef and pork ragu simmered most of an afternoon, béchamel instead of ricotta, and fresh sheets between the layers.
The ragu can wait
Make the ragu a day or two ahead — it is better for it — or freeze it and thaw overnight. That turns this from an afternoon into an hour.
Finely chop the carrot, celery and onion, and sweat them gently in the olive oil in a large, deep pan until soft — about ten minutes. This is where the depth comes from; do not rush it or let it colour.
Add both minces to the softened vegetables and cook until browned, breaking the meat up with a wooden spoon as it goes.
If there is a lot of fat in the pan, spoon some out. Pour in the red wine and let it reduce by half.
A wine you would happily drink with the finished dish — a Sangiovese, a Chianti, a Primitivo.
Once the wine has reduced, add the passata, tomato paste, bay leaves, one litre of the beef stock and a good pinch of salt and pepper. Stir everything together.
Leave it on the lowest heat for two and a half to three hours, uncovered, adding the rest of the stock about halfway through. It should end up thick and glossy, not soupy.
If it tightens too much before the time is up, loosen it with 125 ml of water at a time.
Do not put a lid on it. Covered, it never concentrates, and a wet ragu is what makes a lasagne collapse on the plate.
Melt the butter in a saucepan until it bubbles, then stir in the flour to a paste and let it cook for a minute.
Add half the milk slowly, whisking constantly so it stays smooth. Once it begins to thicken, add the rest along with the nutmeg, the parmesan and a pinch of salt and pepper.
Keep it over the heat, stirring, until it thickly coats the back of a wooden spoon. Take it off and set it aside.
Heat the oven to 180 °C. You want a 9×13 inch dish, or anything close to it.
Spoon a little ragu over the base of the dish, then an even layer of pasta sheets, cut to fit. More ragu until the pasta is covered, then two ladles of béchamel. Repeat until everything is used — four or five layers of pasta — keeping back enough béchamel for the top.
A ladle is about 125 ml, if you would rather measure it than eyeball it.
Tear the mozzarella over the top layer of béchamel and bake for about 45 minutes, until it is bubbling and properly golden.
Give it five to ten minutes out of the oven before cutting. It needs that to hold its shape on the plate.
If a slice still slumps after resting, the ragu had not reduced far enough. Next time, give it the full three hours uncovered.