Lasagne

Onion and garlic go in first and only until the onion softens — not browns. Brown it here and you've built a bitter edge into four hours of sauce you can't fix later; soft and translucent means the raw sulphur compounds have cooked off without the sugars caramelising yet. The mince then wants proper heat, high enough to brown rather than stew in its own juice. That browning — the Maillard reaction, the same thing that happens on a Sunday roast joint — is where the savoury depth comes from; mince added to a timid pan just greys and weeps water, and that water is exactly what waters down your sauce before it's even started.

Carrot, celery and courgette are grated coarsely rather than diced for a practical reason: they dissolve into the sauce over the long simmer instead of sitting there as stubborn chunks, and they're doing a job your nose will recognise as sweetness and body, not as "vegetables in a meat sauce." Courgette particularly is mostly water — it's there to soften and vanish, not for flavour, so don't mourn it if you leave it out; use any soft, watery vegetable you have, or skip it and reduce the sauce a touch longer to compensate.

The wine isn't for flavour as itself — by the time it's simmered for hours you won't taste "wine," you'll taste the acidity it leaves behind, which is what cuts through the richness of the mince and butter later. Any dry wine does this; if you've none open, a splash of vinegar diluted in stock does the same acidic job, just less generously.

For the oil, "olive oil" here is doing nothing an oil with no smell of its own couldn't do just as well, since its character gets cooked out over four hours anyway — sunflower or a light vegetable oil works fine; save a good extra virgin for drizzling raw over something that stays cold.

Butter and flour cooked together before the milk goes in is simply making sure the flour's raw starch grains are coated in fat and cooked through, so the sauce thickens smoothly instead of leaving you with a lumpy, chalky paste — pour cold milk straight onto raw flour and you get exactly that, lumps that whisking alone won't fully rescue. Nutmeg is traditional in béchamel for a reason rooted in cost and history, not magic: it was one of the few warm spices that didn't fight with dairy, and a pinch still lifts milk-based sauces without announcing itself — leave it out and nobody at the table will accuse the dish of anything, but it'll taste a touch flatter.

Mozzarella melted into the béchamel itself, rather than only on top, means the middle layers have some stretch and richness too, not just the top crust everyone fights over. Fresh mozzarella rather than the dry block sold for pizza toppings matters here because fresh mozzarella carries water that helps it melt smoothly into the sauce; the drier block tends to go stringy and separate rather than blend.

At 175°C fan the job left to the oven is modest: finish softening the dried pasta sheets using the moisture trapped between the layers, and colour the top. Twenty minutes is the lower bound, not a deadline — judge it by whether a knife slides into the centre with no resistance from a stiff, uncooked sheet, and by a top that's gone from pale to properly golden, blistered in places. Some say you must pre-cook lasagne sheets first — no, because if your sauces carry enough moisture, dried sheets cook perfectly well in situ, and pre-boiling them just adds washing-up and a risk of tearing fragile sheets before they've even gone in the dish. Let the finished dish sit ten minutes out of the oven before cutting — it's not optional, it's the béchamel setting enough to hold a slice together instead of sliding apart on the plate.