Heat the oven to 180ºC/160ºC fan and grease the inside of the bundt tin making sure that all areas of the inside of the tin are covered leave to the side.
In a large bowl, beat together the unsalted butter and caster sugar until light and fluffy.
Add in the self raising flour, eggs, baking powder and beat again briefly till combined – try not to overbeat! If its really thick, mix in some whole milk to loosen.
Divide the mixture and transfer half to another bowl - beat in the cocoa powder to one of the mixes with a couple of spoonfuls of whole milk if needed. Mix in the vanilla extract to the other plain mix!
Dollop in a tablespoon of each different mix randomly in the tin so you affectively have a bit of everything in a slice - use up all the mix and smooth it over.
Bake for 50 minutes-60 minutes until baked through - check this by poking a skewer into the deepest part of the bundt.
Once baked, leave the cake to cool in the tin for 10 minutes, and then remove carefully and leave to cool fully on a wire rack.
Decoration
To decorate, melt your three different type of chocolates and decorate how you please - As I did the chocolate layer by layer, I needed more dark chocolate for the bottom, but the amounts I used were perfect for the decoration I chose! Sprinkle on some sprinkles and leave to set. Enjoy!
Notes
I melt my chocolates in a microwaveable glass bowl in 30second bursts on a medium power.
I bought my tiered heart bundt tin in TKmaxx where it was cheaper, but you can buy so many different Nordic Ware tins online that it won't be hard to find! I love this one in particular as its so cute and perfect for this kind of bake! If you use a Bundt Tin that isn't as big as the Nordic Ware ones you might want to reduce the cake mixture down as it might over flow.. but this level of mixture is perfect for the large Nordic Ware ones for definite.
This cake will last in an airtight container for 3 days, or you can freeze it for up to 3 months!