• Pre-heat your oven to 160 degrees Celsius. Grease and line the base and sides of three 8 - inch round cake tin with greaseproof paper.
• In bowl of mixer beat butter until smooth, then gradually add sugar and beat until light and fluffy (about 5 minutes)
• Add eggs one at a time, beating well after each addition. Beat in vanilla extract.
• Sift in the flour and baking powder and fold in gently to mix, then add the milk and mix gently to combine.
• Remove half the batter and place in a different bowl and into this bowl, fold in the cocoa powder.
• Take two spoons and use them to dollop the chocolate and vanilla batter into prepared cake tins alternatively. Once all the mixture has been used up, tap the bottom of the tins on your work surface to ensure there aren't any air bubbles.
• Take a skewer or a knife and swirl it through the batter to create a marbled effect. Don't over mix.
• Bake for 25 - 30 minutes or until a toothpick inserted in the centre comes out clean.
• Remove cakes from oven and allow to cool completely on wire rack.

Chocolate Fudge Frosting

• In a bowl of stand mixer or with a handheld mixer, beat the butter on medium speed until pale and fluffy, about 5 minutes.
• With the speed on low, add sifted icing sugar and cocoa powder, hot water, sour cream, vanilla and salt and beat until well mixed, about 1 minute. Increase the speed to medium and beat for 2 more minutes.
• Add the melted chocolate and beat on medium speed until smooth, about 1 minute.

To assemble cake

• Using a serrated knife level each cake by cutting the top.
• Spread a thin layer of icing on your cake board .Place one layer of cake, flat side down on top and plop a big dollop of icing in the middle. Spread the icing carefully. Once it is nice and flat, stack the second cake, flat side down and spread another generous amount of frosting then place final cake, flat side down.
• Spread a thin layer of frosting on the sides and then top of cake. It helps to use a turntable when frosting a cake. Hold a scraper flat against the side of the cake and then turn the turntable and scraper to make a nice, smooth coat of icing. Smooth the top of cake with scraper, drawing the peaks o the top edges of cake into the centre.
• Chill crumb coated cake in fridge for 30 minutes until buttercream is nice and firm.
• Once cake is chilled, cover evenly with buttercream using an off set spatula and then use a scraper to smooth the edges. Pipe decorative shell borders using a 1M nozzle and sprinkle with confetti if desired.