Easter Carrot Cake

Butter should be properly soft, not melted — soft enough to take a thumbprint, still holding its shape. Melted butter won't trap air when you cream it with sugar, and that trapped air is most of what lifts this sponge, since there's no separate whisking of whites into the carrot batter. Cold butter just won't take the sugar in at all, you'll be fighting it for ten minutes and bruising your eggs when you add them. "Room temperature" on a British kitchen worktop in April is not room temperature in August — judge it by feel, not by a clock sitting on the counter.

Carrot: grate it, don't food-process it to a mush. You want fine shreds that still have some structure, because they're there for moisture and a faint vegetal sweetness, not to disappear entirely — a cake with carrot pulverised to paste bakes heavier and wetter in the centre, because the water's already released before it even goes in the oven. Any firm, not-too-woody carrot works; the supermarket bagged ones are fine, you're not hunting down anything special here.

Gelatine leaves versus powder: leaves give you a cleaner set with less chance of lumps, because they're already measured as a sheet — soak, squeeze, melt. If you only have powdered gelatine, bloom it in a little cold water first rather than throwing it straight into something warm, or you get the same stringy-lump problem people blame on "bad gelatine" when it's really bad technique. Five leaves set 150ml of lemon juice plus the egg and cream volume — don't be tempted to add more "to be safe," because over-set mousse turns rubbery and loses the point of being a mousse at all.

Lemon juice, not bottled — 150ml is roughly four to five lemons depending on the fruit, and you want the zest from one of them finely grated, not in strips, so it disappears into the yolk mixture rather than sitting as bitter flecks. Some say you can use bottled juice and nobody will know — no, because bottled juice is often cut and oxidised, and in a dish where lemon is the whole flavour of half the cake, not a background note, that difference is exactly what you'll taste.

Two batches of double cream do different jobs and shouldn't be confused: the 150ml goes into the mousse itself, whipped only to soft peaks — stiffer than that and it won't fold through the egg mixture without knocking the air back out, which is the actual reason mousses turn dense instead of staying light. The 200ml is the outer coating, whipped properly and spread on cold, set cake — this one can go firmer because it's not being folded into anything, it's just cladding.

On the oven: 175°C fan is a genuine instruction, not "medium" dressed up — at that heat the sponge sets from the outside in over roughly 45 minutes without the edges drying out before the centre with its carrot moisture catches up. Check doneness by feel, not the clock: a skewer should come out clean, the top should spring back rather than leaving a dent. Baking tins used for both the sponge and later the mousse layering is just a kitchen without a cake ring talking sense to itself — line it with cling film the second time round so the set mousse releases cleanly, because nothing rescues a mousse that's torn itself against bare metal.

Last thing: the fridge is doing real work here, not just "chilling." A domestic fridge runs around 4°C, cold enough to set gelatine but slow about it — that's why overnight beats four hours if you have the evening to spare. Build this the day before whatever you're serving it for, cut the rosemary nest and decorate in the morning, and you're not racing the cake. Racing it is how slices arrive at the table half-collapsed.