Cream the butter and sugar together until pale and light, using an electric whisk.
Beat the eggs and milk in separate bowl.
Add a third of the egg mixture to the butter and sugar mix, and combine.
Mix flour, cocoa and baking powder in a bowl (you should have 3 bowls in use at this point).
Add a third of the flour mixture to the butter and sugar, and fold in using a metal spoon or rubber spatula.
Continue folding in a third at a time until all of the egg and flour is evenly incorporated.
Spoon the mixture evenly between your cupcake cases.
Place in a preheated oven at 170°C (350°F) and bake for 20-25 minutes until the cakes have risen & the surface springs back to the touch.
To check the cakes have cooked through properly, insert a cocktail stick into the centre, and it should then emerge clean.
Remove from the oven and allow to cool fully before icing.
Place the softened butter in a bowl and sieve a small amount of icing sugar over, before mixing.
Place the cocoa powder in a bowl, add the milk 1 tablespoon at a time until a thick, smooth paste forms, then add it to the butter mixture.
Continue to add the icing sugar in small amounts, adding a little milk to loosen the mixture if needed.
Once you're happy with the texture of the icing, spoon into a piping bag with the nozzle of your choice. Expel any air from the bag and twist the end to make sure the icing cannot leak out.
Holding the twisted end closed, gently apply pressure to the bag and pipe a swirl of icing onto each cake, before topping off with further decoration if desired.
Twist the bourbons apart, remove the cream filling, place biscuits in a bag & crush.
Divide the icing into two even portions, and add 2-3 drops of green food colouring to one until the icing is a consistent colour throughout and you have the shade you desire. Wash your hands before repeating the same process with the second portion of icing and the pink food colouring.
Give your work surface a light covering of icing sugar and roll out the green icing to a width of about 0.3cm (about the thickness of pound coin). Using a leaf shaped cutter, cut out 32 leaves (two per cupcake).
Roll out the pink icing with a 0.3cm thickness. Cut out 16 strips measuring 0.5cm wide and 4cm long, tapering one end with a slanted angle.
Dab a tiny bit of water along the strip and roll up from the tapered end keeping the wet area inside until the strip is fully coiled, and shape between your fingers to create a rose shape.
Sprinkle a teaspoon of the crushed biscuits over each cake, place two leaves onto the icing and gently push the rose in the middle.