Chocolate truffle cake

For the cake, preheat the oven to 180°C. Open and remove the bottom of a 20cm spring-form cake tin. Line with greaseproof paper, reassemble and lightly grease the bottom and sides.

Sift the flour, salt, cocoa powder and baking powder three times in a large mixing bowl and set aside until needed.

Beat the sugar and eggs in an electric mixer until the mixture is pale, thick and tripled in volume, about 10 minutes.

Gently fold in the flour mixture, alternating with the buttermilk. Once combined, mix in the butter and vanilla extract.

Pour the mixture into the prepared cake tin and bake until the cake comes away from the sides, about 30 minutes. Remove from the oven and leave to cool in the tin.

For the filling, combine the chocolate and cream in a pot over low heat, stirring continuously.

Combine the yolks, castor sugar and vanilla in a double boiler and beat until thick and creamy, about 10 minutes. Remove from the heat, fold the chocolate mixture through the egg mixture and beat until cold, about a further 10 minutes. Refrigerate for 30 minutes.

Remove the cake from the tin and cut horizontally. Place the bottom layer back in the tin and pour over the filling. Replace the top layer of the cake and refrigerate until set, about 5 hours or overnight.

Carefully remove the cake from the tin and smooth the edges of the filling with a heated palette knife.

To make the topping, melt the chocolate and butter over a double boiler. Sift in the icing sugar and mix to combine.

To serve, pour the topping over the cake and decorate with the chocolate twirls.