Brooklyn blackout cake

Preheat the oven to 160°C, gas mark 3 and grease and line 3 x 20cm round, loosebottomed sandwich tins. Put the plain flour, brown sugar, cocoa powder and bicarbonate of soda into a large bowl, then whisk to combine. Melt the butter in a small saucepan.

Whisk the buttermilk and milk into the melted butter, then beat in the eggs.

Pour the wet mixture into the dry ingredients and whisk until a smooth batter forms. Evenly scrape the cake mixture into the prepared tins and smooth the tops with a spatula.

Bake for 25-30 minutes, swapping the cakes around for the last 10 minutes, until risen and a skewer inserted into each centre comes out clean. Allow to cool completely before coating

While the cakes cool, make the chocolate custard filling. Combine the milk, caster sugar, golden syrup and cocoa powder in a large saucepan, and warm over a medium heat, stirring occasionally, until the mixture boils.

In a separate bowl, combine the cornflour with 75ml cold water and whisk until smooth. When no lumps remain, slowly pour the cornflour mixture into the saucepan, whisking continuously. Whisk over the heat for 2-3 minutes, until it thickens considerably. Allow to boil for 1 minute, then remove from the heat and stir in the butter and vanilla extract. Pour the mixture onto a parchmentlined baking tray, cover with another sheet of parchment to stop a skin forming, and leave to chill completely

When ready to assemble the cake, use a serrated knife to trim the tops of the cakes so each one is completely level. Place the offcuts into a mini food processor and blitz to crumbs, or crumble between your fingers in a bowl.

Place the bottom layer of sponge onto a cake stand and spread with chocolate custard. Repeat with the remaining 2 layers, then cover the cake completely with custard using a palette knife. Chill for at least 1 hour to solidify. Coat the outside of the cake with the crumbs, then chill until ready to serve. The cake will keep for 2-3 days in the fridge.