Rachel Allen Marbled chocolate crumb cake recipe from the Cake Diaries

Rachel Allen make a tasty looking marbled chocolate crumb cake from her Cake Diaries.

The ingredients are 225 g (8oz) butter (softened, plus extra for greasing), 225 g caster sugar, 4 eggs, 1 tsp vanilla extract, 225 g plain flour, 2 tsp baking powder, 50 ml milk, 25 g cocoa powder and icing sugar, for dusting.

For the crumble topping: 125 g plain flour (sifted), 75 g caster sugar, 75 g unsalted butter, chilled and cut into cubes, 75 g dark or milk chocolate, 23 cm diameter spring-form or loose-bottomed cake tin with 6cm.