Raspberry Custard Crostata

For the base: 300 g plain flour is just flour, nothing fancy, the same bag you'd use for a Victoria sponge or Sunday roast gravy. The butter has to be cold and cubed — straight from the fridge, not softened on the counter — because its job is to stay as separate flecks through the mound-and-well method, not melt into a paste. If your kitchen is warm, work fast, or even chill the flour too; a hot summer afternoon is the enemy of short pastry more than any recipe step is. One whole egg plus one yolk (you'll use the other three yolks in the custard) bind the dough without making it wet — egg yolk carries fat, which keeps pastry tender, while the white in the whole egg gives it just enough structure to hold a shape without cracking when rolled.

Rolling to 4-5 mm matters more than it sounds: thinner and the base turns brittle and cracks when you lift the finished tart; thicker and you get a doughy, underbaked ring where the custard sits, because the centre of a 26-28 cm tart never gets the direct heat the rim does. Pricking the base with a fork before baking isn't decoration — it lets steam escape through those little tunnels instead of building up under the dough and pushing it into a dome, which would give you an uneven surface for the custard to sit in. If you don't own a proper crostata tin, a loose-bottomed flan tin from the baking aisle does the same job — the removable base is the real requirement, not the shape, because you need to get a delicate shell out without cracking it, and a solid tin leaves you prising at pastry with a palette knife and a prayer.

The custard is just milk, sugar, egg yolk and flour cooked slowly until it thickens — the same family as the stuff under a trifle, so if you've ever made that, you know the texture you're aiming for: it should coat the back of a spoon and hold a line when you drag a finger through it. The trick, and the only real trick in it, is temperature control on an ordinary hob: bring the milk to the boil first so it's hot when it meets the egg-sugar-flour mix, then cook the combined lot on low heat, stirring constantly. Some say a bain-marie is essential for custard — no, because what actually curdles egg yolks is a sudden jump to high heat, not the absence of a water bath; constant stirring on a gentle flame does the same protective job, and it's one less pan to wash in a flat that doesn't have a kazan-sized hob to spread pans across. Flour here (rather than cornflour, which some versions use) gives a slightly denser, more cuttable set — fine for a tart you want to slice cleanly rather than spoon.

If you're out of plain caster sugar for dusting, icing sugar from the baking cupboard is interchangeable at this stage — it's only there for a last dusting on top, not for sweetening anything that's already cooked. And if raspberries are out of season or the ones in the shop look sad and pale, any soft summer berry — strawberries halved, blueberries whole — sits on custard the same way; the raspberry's only non-negotiable job is tartness against all that sweet custard and short pastry, so whatever you swap in, keep something sharp.

Patience is the actual ingredient that makes or breaks this, more than any single step. The dough needs its chill, the custard needs its slow stir, and the baked shell needs to go stone cold before you fill it — rush any one of those and you're eating something that tastes fine but falls apart on the plate. This isn't a tart you build in one sitting after work; it's one you start the base for at lunchtime and finish for tea.