Blueberry Mousse Cake with Glaze

Start at the base. Digestive biscuits plus almonds plus butter is the English version of a pâte sablée crumb crust — cheap, no oven skill required, and it holds together purely because melted butter glues crumbs into a solid once it re-hardens in the fridge. The liquorice powder is doing something specific: against blueberry's sweet-sourness, a thread of aniseed-bitter liquorice reads as depth rather than as "what is that flavour", the way a pinch of salt does in caramel. Leave it out if you can't find it — you won't break the cake, you'll just lose a layer of complexity nobody will miss by name. Any plain, not-too-sweet biscuit works here; digestives are just what's in a British cupboard. Ginger nuts would do the same structural job and echo the liquorice's warmth instead of fighting it.

The sponge is a basic creamed batter — butter and sugar beaten to trap air, which is the only rise this gets besides the baking powder, so don't rush the beating stage thinking it's just mixing. Marzipan here isn't a decoration ingredient borrowed from Christmas cake; grated into a sponge batter it melts into pockets of almond-sugar paste that keep the crumb moist for days in the freezer, which plain sponge won't do — frozen plain sponge goes chalky and dry on thawing, marzipan-enriched sponge doesn't, because the sugar and oil in it resist ice crystal damage. Some say marzipan is only for icing a cake's exterior — no, because its job here is structural and has nothing to do with looks.

The mousse is built the way all mousses are: a flavoured base (the blueberry purée) carries the gelatine, and whipped cream is folded in only once that base has cooled to room temperature. Fold warm purée into whipped cream and you deflate the air you just worked for — the cream collapses back to liquid around the heat, and you get a dense, wet mousse instead of a light one. This is the same reason you cool custard before adding cream anywhere else. Gelatine leaves are preferred over powder in a recipe like this because leaves give a cleaner, more reliably set result without the grainy texture powder can leave if it's not bloomed properly — but if you only have powder, the fix is a criterion, not a swap: bloom the equivalent weight in a little cold water first, then melt it exactly the same way, over heat gently enough that it never boils, because boiled gelatine loses its setting power entirely.

The glaze is where people go wrong, and it's worth saying why the blending technique matters as much as the temperature. Running the stick blender diagonally, keeping it submerged, never lifting it mid-blend — that's not showmanship, that's the only way to emulsify chocolate and hot milk-syrup into a stable mixture without beating air into it. Air bubbles in a glaze don't disappear; they sit on the cake's surface as little craters once it sets, and no amount of smoothing fixes that after the fact. The glucose syrup's job is to keep the glaze glossy and slow down sugar crystallising as it cools — golden syrup is the nearest thing in a British kitchen, though it'll pull the colour and flavour slightly, which matters if you're going for a pure white base before adding colouring.

For a 16 cm sponge sitting inside a 20 cm mousse mould, you're not making a cake that's mostly sponge — you're making a mousse cake with a lemon-sponge disc as its anchor, which is why the sponge recipe is modest and the mousse recipe is generous. Ten servings out of this is realistic because it's rich and cold; it cuts in thin, clean wedges straight from frozen-glazed rather than crumbling the way a room-temperature sponge cake does, and that's also the real reason you serve it this way rather than letting it sit out and go soft before cutting.