Chantilly Cake

Ingredient by ingredient, start with the eggs — four whole, five yolks on their own later for the custard. Buy them at room temperature if you can, or let them sit out an hour; cold eggs trap air reluctantly, and you're relying entirely on air here. Caster sugar, not granulated, because its smaller crystals dissolve into the egg before the mixer's done its work — granulated can leave you with a faint grit in the crumb, not a catastrophe, but pointless when caster costs the same.

Flour and potato starch together, roughly equal weight. If you have no potato starch, cornflour does the same job — both are pure starch with no gluten to contribute, and the point is to cut the flour's gluten down, not to add flavour. Don't swap in self-raising flour thinking it'll help the rise: there's no benefit here, because the lift is coming from whisked air, and the extra raising agent will just make the crumb coarser and less able to hold its shape when sliced thin.

For the custard: whole milk, not semi-skimmed, because the fat is what gives the set body instead of a thin, watery sauce. A vanilla pod split into the milk while it heats pulls flavour out slowly as it steeps — vanilla extract works as a stand-in, stirred in once the custard's off the heat, but you lose the little black flecks that tell people, correctly, that someone used a real pod. Cornflour is the thickener; egg yolks alone would need far more of them and far gentler heat to set a custard this thick without scrambling, so the starch is doing the heavy lifting and protecting the yolks from themselves.

Double cream, whipped with sugar and vanilla to soft peaks, not stiff — stiff cream folded into custard turns grainy and starts weeping liquid by the next day, because you've already broken the fat structure before it ever met the custard. Folding a third of that cream into half the custard makes the diplomate — a cream with enough body to hold a layer but soft enough to still feel like custard in the mouth, not jelly. The remaining plain whipped cream coats the sides and top; some recipes call this "chantilly cream," which is where the cake gets its name — not a place, not a person, just a style of sweetened whipped cream that happens to be French.

Milk brushed onto each sponge layer before the cream goes on is the unglamorous fix for a real problem: a génoise with no syrup or liqueur soak dries out fast, especially the cut edges exposed to fridge air. A spoonful of milk, not cream, not syrup — just enough to put moisture back without adding sweetness you don't need, since the cream's already sweet.

On equipment: you don't need a kazan or anything exotic for this one, just an electric mixer with some patience behind it, a 22cm tin, and a serrated bread knife for the slicing — a chef's knife will drag and crush the crumb instead of cutting clean lines. Chilling at the end isn't optional waiting around; the cream layers need the fridge's cold to firm up enough that the cake holds its shape when you cut it, rather than slumping sideways on the plate. Give it the time. That's patience doing the work heat can't.