Heat your oven to 180ºC/160ºC Fan and line a cupcake/muffin tin with 12 large cupcakes cases/muffin cases.
Beat the unsalted butter with the light brown soft sugar until light and fluffy.
Mix the eggs, self raising flour, cocoa powder and melted milk chocolate with the butter/sugar mix until well combined. It won't take too long to mix!
If the mixture is too stiff you can add a little bit of whole milk 1tbsp at a time to get a smooth light consistency (Full-fat will prevent the mix splitting).
Add in the milk chocolate chips, and fold them though evenly.
Spoon the mix into the cupcake cases evenly and bake in the oven for 18-22 minutes or until a skewer poked into one of the cakes comes out clean and they are springy to touch, then leave them to cool fully on a wire rack.
Buttercream
Melt the white chocolate and dark chocolate in separate bowls over a pan of simmering water, or in the microwave in short bursts and leave to cool on the side for 10 minutes.
Beat the unsalted butter with an electric mixer for a couple of minutes to loosen it, then beat in the icing sugar until well combined (this can take up to 5 minutes).
Split the mixture into two bowls, and add a melted chocolate to each bowl and mix to combine.
Decoration
Add the two buttercream to a large piping bag with your favourite piping tip - I get a large piece of clingfilm, add each flavour of buttercream in a line, roll the clingfilm up tightly to a sausage, snip off the end, then add this to the piping bag.
Pipe the buttercream on to the cupcakes and decorate with some sprinkles.
Notes
I used 100% cocoa powder, milk chocolate chips, and white and dark chocolate buttercream to get my triple chocolate fix, but you can of course use whatever cocoa powder you like, whatever dark/milk/white chocolate chips you like - and even a different chocolate in the frosting - but this combination is the ULTIMATE.
These cupcakes will last in an airtight container for 3 days at room temperature, or you can freeze them for up to 3 months!