For the ragu, heat the oil in a large saucepan over a high heat and add the grated vegetables. Fry for about 5 minutes,stirring frequently until very fragrant. Add the tomato paste and fry for about 2 minutes. Add the pork,beef and pancetta and stir to coat. Add the wine,tomatoes,bay leaves,salt and pepper,and bring to a simmer. Continue to simmer partially covered for 1½ to 2 hours,stirring occasionally and topping up with a little stock or water if it starts to look too dry.
For the bechamel sauce, stir the butter and flour in a small saucepan over a medium heat for 2 minutes until foaming,then add the milk a little at a time,stirring constantly to remove lumps until a thin sauce is produced. Simmer for 5 minutes,then stir in the salt and nutmeg.
Cook the spaghetti in plenty of boiling salted water according to the packet directions. Drain well and toss a third of the ragu bolognese through the drained pasta.
Share the pasta across 4 serving plates. Top each portion with alternating spoonfuls of the ragu and the bechamel,and finish with a little grated parmesan.
Tip
To get maximum flavour from your spaghetti in this dish,cook it until almost al dente,then add it to one third of the ragu with a little of the pasta water over a medium heat and finish it that way.