For our ‘Sweet Treat’ feature, we bring you a taste bud-tingling, saliva-inducing recipe every week. Whether you simply want to put your baking skills to the test or fancy treating your colleagues to something tasty (hint hint Her.ie girls!), this is where to come. This week, it’s Marbled Chocolate Crumble Cake courtesy of Rachel Allen's Cake book...                                                                                                     (Serves 6-8) Ingredients: 225g butter, softened, plus extra for greasing 225g caster sugar 4 eggs 1 tsp vanilla extract 225g plain flour 2 tsp baking powder 50ml milk 25g cocoa powder For the crumble topping: 125g plain flour, sifted 75g caster sugar 75g unsalted butter, chilled and cut into cubes 75g dark or milk chocolate, in chips or roughly chopped into pieces 23cm diameter spring-form or loose-bottomed cake tin with 6 cm sides   Method: 1. First make the crumble topping. Using your fingertips, rub together the flour, sugar and butter in a large bowl until it resembles thick breadcrumbs, then mix in the chocolate pieces. Set aside in the fridge while you make the sponge. 2. Preheat the oven to 180 degrees/ gas mark 4, and butter the sides and the base of the cake tin. If you’re using a spring-form tin, make sure the base is upside down so there’s no lip and the cake can slide off easily when cooked. Cream the butter until soft in a large bowl or in an electric food mixer. Add the sugar and beat until the mixture is light and fluffy. 3. Whisk the eggs and vanilla extract together in a small bowl for a few seconds or just until combined, then gradually add the eggs to the creamed butter and sugar mixture, beating all the time. Sift in the flour and baking powder and fold in carefully, then add the milk and mix gently to combine. Tip half of the cake mixture into another large bowl, then sift the cocoa powder into this bowl and fold it in. 4. Place the two different cake mixtures in the prepared tin by alternating heaped tablespoonfuls of the vanilla batter with the chocolate one. Then, with a skewer or similar implement, gently draw swirls through the cake mixture to ‘marbleise’ it. Try not to over-mix or you won’t get that wonderful marbled effect. 5. Scatter the crumble mixture evenly over the top of the cake mixture and bake for 50-60 minutes or until the crumble is golden and a skewer inserted into the centre of the cake comes out clean. 6. Remove from the oven and allow to cool in the tin for 10 minutes. Then loosen around the edges using a small, sharp knife and remove the sides of the tin. Place the cake (sitting on the base of the tin) on a wire rack and allow to cool completely. 7. Use a palette knife or metal fish slice to loosen the bottom of the cake from the base of the tin. Then slide the palette knife or fish slice under the cake and carefully ease it onto a plate. Dust with icing sugar to serve.