Lasagne al Forno

1. 1Make the ragù first — it can be done days ahead, and a cold ragù spreads more evenly than a hot one.
2. 2For the béchamel, melt the butter, stir in the flour and cook over a medium heat for 2 minutes until it smells biscuity rather than raw. This is a blond roux: stop before it takes colour.
3. 3Pour in the warm milk a third at a time, whisking hard until smooth before the next addition. Cold milk into hot roux is the usual cause of lumps.
4. 4Add the bay, nutmeg, salt and a little white pepper and simmer gently for 8 minutes, stirring, until it coats a spoon and holds a line when you draw a finger through it. Fish out the bay.
5. 5Heat the oven to 180°C fan. Spread a thin scrape of béchamel in a 30 x 20 cm dish — just enough to stop the first sheets sticking.
6. 6Build six layers: pasta, a thin spread of ragù, a thin spread of béchamel, a scatter of Parmesan. Thin is the whole instruction. Each ragù layer should barely cover the pasta beneath it; heap it on and the lasagne will not hold together when cut.
7. 7Finish with pasta, all the remaining béchamel and a generous layer of Parmesan. The top wants more béchamel than the inner layers so it browns rather than dries.
8. 8Bake for 40–45 minutes, until browned and blistered and bubbling slowly at the edges. If the top colours too fast, cover it loosely with foil for the last 15 minutes.
9. 9Rest for a full 20 minutes before cutting. Straight from the oven it is molten and will collapse; after 20 minutes it sets enough to hold a square.

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