250g dark chocolate (at least 70% cocoa solids), chopped
160g unsalted butter, cubed
175g caster sugar
2 tsp vanilla extract
140g ground almonds
6 egg yolks
6 egg whites
Icing sugar, to dust
Preheat the oven to 180 C / 160 C fan. Grease and line a 23 cm springform tin and set aside.
Melt the chocolate, butter and sugar together in a heatproof bowl set over a pan of simmering water. Stir until smooth and completely melted together, remove from the heat and leave the cool down for 5 minutes then mix in the vanilla, almonds and egg yolks, one at a time.
In a medium sized bowl whisk the egg whites until medium-stiff peaks form. Use a large metal spoon to fold 1 spoonful of egg whites into the chocolate mixture to loosen then fold the rest of the egg whites into the mixture gently, taking care to keep as much air in the batter as possible. Spoon into the prepared pan and smooth the top.
Bake for about 30 minutes, until puffed, but still a little wobbly in the middle. Cool completely in the tin then remove and dust with icing sugar before serving.