Brooklyn blackout cake

1.Preheat oven to 170°C. Line the base of a 20cm-diameter cake tin with baking paper. Bring dates and 350ml water to the boil in a saucepan, add bicarbonate of soda, then purée with a stick blender until smooth.

2.Beat sugar and butter in an electric mixer until pale and creamy. Beat in eggs, then stir in the date purée. Sift together dry ingredients, fold into butter mixture, then pour into tin. Bake until an inserted skewer comes out clean (50 minutes to 1 hour). Cool in the tin, then turn out and slice horizontally into 5 thin layers (about 5mm); hold your knife steady while rotating the cake to get even layers.

3.For ganache, place chocolate in a heatproof bowl and bring cream to the boil. Pour cream over chocolate, stir until melted and smooth, then chill for 30 minutes. Transfer chocolate mixture to an electric mixer and whip until light and fluffy (10 minutes). Chill for 15 minutes, then whisk until light and airy (15 minutes).

4.Place a disc of the cake in a lined springform tin and top with a layer of ganache. Alternate the layers, finishing with ganache. Smooth the top, refrigerate until set (2-3 hours), then dust with cocoa and serve. Cake will keep refrigerated for up to 5 days in an airtight container.