Raspberry Mousse Cake on a Chocolate Base

Think about why this shape of recipe exists at all. A mousse this soft can't hold its own weight on a plate — it needs either a container or a cold surface to set against. The freezer and the silicone mould are doing the job that a proper French pâtisserie would do with a metal ring and careful chilling in a blast freezer; at home, a springform tin for the base and a loose silicone mould for the mousse are the honest stand-ins. A silicone mould matters here for one reason only — it releases the frozen mousse cleanly without you having to run a tin around the edge and risk tearing the dome, which a rigid cake tin would do.

Butter: melt it gently, don't let it brown or spit, because this isn't a recipe that wants nutty butter flavour fighting the chocolate — it wants fat that carries the chocolate smoothly into the eggs without seizing it. If the butter's too hot when the chocolate goes in, the chocolate can split and go grainy rather than glossy; that's the real reason for taking the pan off the heat first.

Eggs and sugar whisked until pale: this is what gives the base its only lift, since there's barely any flour here to hold structure. Whisk them properly — pale and thick, ribbon stage — because this trapped air is the entire difference between "dense cake" and "chocolate brick." The ground almonds replace flour almost entirely; they add structure without the gluten that would make the base chewy rather than fudgy, and they're also the reason this base stays moist rather than drying out the way a flour sponge would.

Dark chocolate: use something you'd actually eat off a bar, not a baking chocolate with waxy filler — around 60-70% cocoa solids gives bitterness that balances the sweet raspberry mousse above it. Go too mild and the base reads as just "more sweetness," which the cake doesn't need.

Gelatine leaves: these exist to give the mousse just enough backbone to stand as a cake rather than slump as a trifle. Four leaves for this volume of cream and purée is a light set deliberately — a mousse that's too firm turns rubbery, loses the point of being a mousse at all. If leaf gelatine isn't to hand, powdered gelatine works as a substitute by weight (roughly 2g powder per leaf), bloomed in a few spoonfuls of cold water instead of a bowlful.

Raspberries, frozen rather than fresh, for the purée: frozen fruit is picked and frozen at peak ripeness, so you get more consistent flavour and colour out of season than from fresh berries that travelled a long way to your shop — one of the few places where frozen genuinely beats fresh, not a compromise. The lemon juice and zest aren't there to make it taste of lemon; raspberries lose acidity when cooked, and the lemon pulls the brightness back so the mousse doesn't taste flat and purely sweet. Sieving out the seeds isn't fussiness — leave them in and every mouthful of mousse has a faint grit that fights the smoothness it's meant to have.

Double cream, whipped to soft peaks and no further: any fresh cream with enough fat to hold air works — in the UK that's double cream, full stop, nothing lighter will whip stiff enough to carry its own weight once folded with purée. Whip it past soft peaks and you're folding little grains of butter into your mousse instead of air; that shows up as a slightly curdled texture once frozen and thawed. Fold, don't stir — stirring knocks the air straight back out, and that air is the only thing standing between "mousse" and "raspberry jelly."