Preheat the oven to 180C, 160C fan, gas 4. Place the cupcake cases into the muffin tin.
Mix the eggs, oil, water and cake mix gently together and whisk (by hand or electric mixer) for 2-3 minutes until smooth and creamy.
Pour the mixture evenly into the cupcake cases.
Bake in the centre of the oven for 15-17 minutes or until a rounded knife inserted into the centre of a cupcake comes out clean. Remove and let cool on a wire rack.
Meanwhile heat the cream to almost boiling. Place the chocolate into a bowl and pour the hot cream over the top. Stir until the chocolate has all melted into the cream. Let cool until room temperature.
Hollow out a little of the centre of the sponge and fill with 1 tsp of chocolate ganache. Repeat with all the cupcakes.
Whisk the icing sugar and softened butter together until blended then beat in any of the ganache that was leftover from filling the cupcakes. Spoon into a piping bag with a star nozzle.
Pipe the icing onto the cooled cupcakes and decorate with the chocolate flakes for a perfect finish!