Instructions
1Start the ragù — it needs three hours and it is the whole dish, so give it the time. Warm the olive oil in a heavy Dutch oven over medium and cook the pancetta 4-5 minutes until its fat renders out. Add the onion, carrot, and celery and cook gently 10-12 minutes, stirring often, until soft and sweet. Don't rush this and don't let it brown hard.
2Raise the heat to medium-high and add the beef and pork. Break the meat up with a wooden spoon and cook until it has lost all its raw color, 8-10 minutes. Season with salt and pepper.
3Pour in the white wine and let it bubble until the sharp alcohol smell is gone and the pan is nearly dry, about 5 minutes. Stir in the tomato paste and cook it 2 minutes, then add the passata and the broth.
4Add the milk. This is the step people skip and it is the one that matters — the milk tenderizes the meat and rounds off the tomato's edge, which is exactly why a real bolognese doesn't taste sharp or acidic. Bring to a bare simmer, then drop the heat as low as your burner goes.
5Simmer uncovered 3 hours, stirring every 20-30 minutes and adding a splash of broth or water any time it looks dry. It's ready when it's thick, glossy, and a deep brick color, with the fat just beginning to separate at the edges. Taste and season well — under-salted ragù makes flat lasagna.
6In the last 20 minutes of the simmer, make the besciamella: melt the butter in a saucepan over medium, whisk in the flour, and cook 2 minutes without letting it color. Add the warm milk in a slow stream, whisking constantly. Cook 6-8 minutes until it thickens to the texture of heavy cream, then whisk in the nutmeg and salt. Press plastic wrap directly onto the surface so it doesn't skin over.
7Heat the oven to 375°F and butter a 9x13 baking dish. If you're using dried sheets that aren't no-boil, cook them in well-salted water 2 minutes short of the package time, then lay them flat on a lightly oiled sheet pan so they don't stick together. Fresh sheets go in raw.
8Assemble six thin layers, not four thick ones — this is what separates real lasagna from a casserole. Start with a smear of ragù on the bottom, then repeat: pasta, a thin layer of ragù, a thin layer of besciamella, a scatter of Parmigiano. Keep each layer restrained. Finish with pasta, the last of the besciamella, a heavy blanket of Parmigiano, and dot the top with butter.
9Bake 40-45 minutes, until the top is browned in patches and the edges bubble. If it's pale at 40 minutes, run it under the broiler 2 minutes — watch it the whole time.
10Rest it 15-20 minutes before cutting. Cut it hot out of the oven and it will slump onto the plate. This wait is part of the recipe.