Cream the butter and sugar until light and fluffy, then slowly add the eggs with a little flour.
Preheat oven to 300°F (150°) and prepare a cupcake tin with liners.
Fold in the remaining flour, banana, melted dark chocolate, chocolate chips, orange zest, a pinch of salt and baking powder.
Pour the mixture into a prepared cupcake tin, filling ⅔ of each mould. Top each cupcake with a pinch of caster sugar.
Bake the cupcakes for 18-20 minutes, or until a skewer comes out clean.
Cool in the tin for 10 minutes, then remove the cupcakes from the tin and transfer them to a wire rack.
In the meantime, prepare the frosting. Place the butter into a large bowl and beat with an electric hand mixer until light and fluffy.
Add icing sugar and beat until combined.
Add the milk and the vanilla, then beat until creamy and smooth. Add a pinch of orange zest and pour the mixture into a piping bag with your favorite nozzle.
Frost each cupcake, then top with shaved dark chocolate and 3 mini eggs.