Put the caster sugar and softened butter in a large mixing bowl. Beat them with an electric mixer or by hand until creamy.
Crack the eggs into the bowl. Beat again until just combined.
Add the flour, baking powder and cocoa powder. Fold everything together - the batter will be quite thick at this stage.
Add the milk and mix through again. This will loosen the batter.
Line a 12-hole muffin tray with muffin cases. Divide the batter evenly between them, making sure to level off so that the cupcakes rise evenly.
Push a mini Creme Egg into the centre of each cake, almost to the bottom. Spread the batter over the tops.
Bake for about 20 minutes or until risen and firm. A skewer pushed into the centre of a cupcake towards the middle of the tray should come out clean. Transfer to a wire rack and leave them to cool completely.
Make the buttercream
Put the butter, icing sugar, cocoa powder and water in a large mixing bowl. Start beating them together, slowly at first and then building speed once the icing sugar isn't loose. Keep beating until light and smooth – it’s quickest to use an electric whisk or stand mixer for this.
Make the chocolate drizzle
Grab three microwave safe bowls. Put the milk chocolate in one and divide the white chocolate between the other two. Melt in the microwave (in 30 second bursts) or over a bain-marie.
Colour one of the white chocolate bowls orange.
Putting it all together
When the cupcakes are completely cool, transfer the buttercream into a piping bag fitted with a star nozzle and pipe tall swirls on top of each cupcake.
Drizzle with the three shades of melted chocolate.
Scatter with the chopped Creme Eggs to finish.
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Notes
It's not a good idea to leave these cakes out on the counter for long periods of time as this will cause the sponge to dry out. In addition, you may find the liquid insides of the Creme Egg pieces start to drip down the cakes.Make sure to cover the cakes well and pop them in the fridge asap after making. This will keep the cakes fresh for 3-5 days.