Lemon Meringue Tart

Flour, butter, sugar, egg, baking powder, salt, lemon zest — that's the base, and every one of them has one job. Plain flour, not strong bread flour: you want no stretch, no chew, because this is a biscuit base, not bread. The butter must be cold going in and the dough rested cold after, because warm butter means a dough that slides rather than holds a wall 2.5 cm high — and a collapsed wall is how curd ends up leaking over the sides of your tin instead of sitting in it. Baking powder here is a small insurance policy, giving the base a slight lift so it doesn't bake into something leathery; leave it out and you get a denser, more biscuity shell, which isn't wrong, just different. Lemon zest in the dough is a quiet echo of the filling — rub it in with your fingers against the sugar if you can, that bruises the oil out of the skin rather than just scattering dry flecks through the dough.

The curd is built from lemon zest and juice, egg yolks, sugar, cornflour, water and butter, and here the quantities are doing real chemistry. Three lemons, zested and juiced, give you both the aromatic oils (zest) and the acid and bulk (juice) — zest alone tastes thin, juice alone tastes flat. Cornflour mixed into cold water first, always, because dropped straight into a hot pan it clumps into little gel balls instead of dissolving smooth — that lump you sometimes bite into in a bad curd, that's cornflour that never got a chance to hydrate. The egg yolks go in once the cornflour mixture has already thickened the base slightly, because yolks in a pan that's still too fierce will scramble before they've had a chance to enrich the curd — you're using the starch as a buffer that lets you cook the eggs gently rather than violently. Butter goes in off the heat, in pieces, not because of tradition but because melting it slowly stops it splitting the fat out from the curd, which is how you get that slightly greasy sheen on a bad lemon tart. If you've no cornflour, any pure starch — cornstarch by another name, or potato starch at a pinch — does the same binding job; just don't swap in plain flour, which needs longer cooking and brings its own taste with it.

The meringue needs egg whites, sugar, water and a pinch of salt, and the method — hot syrup whisked into foaming whites — is what separates this from the meringue on a pavlova. Dissolving sugar in water without letting it caramelise means you're after a clear syrup, not a toffee: the moment you see the first proper bubbles, that's your cue, not a clock. Pour it in a thin stream onto whisking whites and you're pasteurising the whites and setting their structure at the same time, which is why this meringue survives sitting cold in a fridge for two hours without turning watery at the base — an ordinary French meringue, just whites and sugar whisked raw, would start weeping liquid under its own weight by then. The drop of lemon juice in the whites before whisking isn't for flavour, it's acid helping the proteins unfold and hold air more stably — cream of tartar does the identical job if that's what's in your cupboard.

Some say you need a kazan or a professional kitchen for a tart like this — no, because a wide domestic pan and an ordinary 20 cm springform tin do the job; the things that actually matter are temperatures and states, not equipment you don't own. Your home oven at 180°C and a cook's blowtorch bought for £15 are entirely sufficient; what you can't substitute is patience — the two hours of chilling the dough, the full cooling of the baked shell before curd goes anywhere near it, the two hours setting in the fridge at the end. Rush any of those and you're not saving time, you're borrowing structural failure for later: a curd that slides off a warm shell, a meringue that slumps because the curd beneath hasn't set. This feeds six, cut in thin wedges — it's rich enough that nobody's asking for a second slice the size of the first.