180g unsalted butter, diced plus extra for greasing
300g golden caster sugar
3 eggs
1tsp vanilla extract
50g cocoa powder
1tsp baking powder
1tsp bicarbonate of soda
280g plain flour
200ml whole milk
Instructions
Start by making filling. Blend cornflour with 200ml milk until smooth. Bring remaining milk to boil in small saucepan with sugar, syrup and cocoa, whisking until smooth. Add cornflour and milk mixture and bring to boil, stirring constantly until have rich, thick custard. Remove from heat and add vanilla and butter, stirring until melts and is smooth (if seems lumpy, give it a whizz in food processor). Pour into large bowl, cover surface with clingfilm and set aside to cool.
Preheat oven to 190C; grease 2*20cm loose-bottomed cake tins (at least 5cm deep) and line with baking parchment. Cream butter and sugar together in food processor, then incorporate eggs one at a time. Add vanilla, scraping down sides of bowl as necessary. Sift together dry ingredients and add half at a time to creamed mixture. Finally add milk with motor running. Divide mixture between cake tins and smooth surface of each. Bake for 30-40mins until skewer inserted into centre comes out clean. Run knife around collar of each cake and leave to cool.
When cakes are cold, slice each one in half lengthways using bread knife. To make blackout, whizz one of top halves to crumbs in food processor. To assemble cake, leave one of cake bases on tin base. Place on wire rack set over sheet of foil (to catch excess custard and crumbs). Spread this with one quarter of custard, taking it almost to rim. Sandwich with remaining cake base (removed from tin) and spread another quarter of remaining custard over surface. Top with last layer of cake and use rest of custard to coat top and sides. To finish, liberally coat whole thing with crumbs and transfer carefully to serving plate. Chill for at least 2hrs, then remove from fridge 15-30mins before eating.