Preheat the oven to gas mark 4 or 180 degrees.
Line a loaf tin with baking/greaseproof paper.
In a large bowl, cream together the butter and sugar (you may want to leave the stork baking block out of the fridge for a while first to soften to make it easier).
Gradually add the eggs and self-raising flour while folding.
Add the zest of two oranges and the juice of one.
Split the mixture into two bowls (I had two thirds to become chocolate, and one third as plain orange).
To the chocolate mixture, add the cocoa powder and the crushed Terry's Chocolate Orange Mini Eggs. Crush these in the packet using a rolling pin.
To the remaining sponge mixture, add the orange food colouring and mix well.
Spoon the two mixtures into the loaf tin, alternating each so that you have a marble pattern.
Smooth the top with a spatula and place in the oven. Bake for 45-55 minutes. Use a cake tester/skewer and once it comes out clean, you know the cake is ready to come out the oven.
Leave to cool.
Make the buttercream by mixing the icing sugar, butter and cocoa powder in a bowl.
Pipe this in a swirl pattern across the top of the cake.
Place an assortment of orange mini eggs (Terry's Chocolate and Smarties) into the icing. Smash a few so that you can sprinkle the fragments to the edges.
Finally, melt the milk chocolate (I did this in a microwave, checking on it every so often). Once melted, pipe through a fine nozzle and drizzle across the whole loaf.
Leave the chocolate to set, then cut a big slice and enjoy!