Vegetarian Cannelloni

The vegetables: aubergine is the one that needs respect, because unlike courgette or pepper it has genuine bitterness locked in its flesh along with a sponge-like structure that soaks oil rather than frying in it. Dice it small and cook it properly rather than hoping heat alone will fix it — if it still tastes bitter or feels spongy rather than soft when you bite a piece, it needs more time in the pan, not more seasoning. Courgette and pepper are forgiving; they mostly need not to be raw in the middle and not to have turned to mush — pepper should bend, not snap, courgette should give slightly, not collapse. Onion goes in first and alone because it needs longer at a gentler heat to go from sharp to sweet — going from pale gold toward amber, never dark brown, which would mean sugars burning rather than caramelising, and burnt sugar reads as bitter in the finished dish, not rich.

Butter and flour in equal weight is the classic roux ratio, and it's not arbitrary — that ratio is what gives you a sauce thick enough to cling to pasta without sliding off, at the volume of milk given here. If you're out of butter, any flavourless fat that can hold flour in suspension will do the same mechanical job — but butter also contributes its own mild dairy fat flavour that oil doesn't, so with oil the sauce works structurally but tastes thinner. Plain flour, not self-raising — the raising agent in self-raising flour has no purpose in a sauce and can give an odd aftertaste. If you have no flour at all, cornflour slurry can thicken milk, but it sets differently — glossier, more jelly-like when cold — so it's a repair, not an equal substitute.

Parmesan appears twice and does two different jobs. Inside the filling, mixed into the vegetables with a little béchamel, it's there to bind and season — a hard, salty, aged cheese melts into the mix and seasons from within rather than sitting on top. On the outside, sprinkled before baking, its job is to brown — the proteins and fats in aged hard cheese catch heat and colour fast, giving you that spotted golden surface rather than a wet one. Any hard, well-aged cheese that melts and browns under heat can stand in — a mature Cheddar will do it, though it will taste more like itself and less neutral than Parmesan.

Lasagne sheets here are doing double duty — they need to be pliable enough to roll around a strip of filling without cracking, which usually means briefly softened in hot water first if you're using dried sheets, since dry pasta straight from the box will crack rather than curl. Fresh lasagne sheets roll more easily if you can get them, but dried is what most kitchens have, and it works once softened.

On oven and heat: "200°C fan" means air moving hard around the dish, which is what gets a browned, slightly crisp top on béchamel in under twenty minutes rather than the hour a static oven might need to do the same job by slow evaporation. If your oven is conventional rather than fan, expect to add heat or time to get the same surface — the mechanism you're chasing is browning on top, bubbling underneath, not a clock number.

One honest note for a domestic kitchen: a kazan-style wide pan isn't needed here at all — a wide frying pan and a deep saucepan cover the whole job, and a baking dish you'd normally reach for after a Sunday roast is exactly the right shape for rolling cannelloni into rows. The one thing no oven glove fixes is rushing the vegetable fry — give it the full stretch uncovered, because that's the only point in the recipe where water has to leave and can't be baked out later. Patience there is the ingredient the rest of the method assumes you've already added.