Preheat oven to 175 C (350 F)
In a bowl, using an electric whisk, whisk together the egg and the sugar until smooth and there's no lumps left. Add milk, butter, vanilla and peppermint to the mixture and mix until combined.
Add the dry ingredients (flour, cocoa, baking soda, salt) and mix with the mixture until well combined and there's no pockets of flour or cocoa. Stir in sour cream.
Either grease a cupcake tin or line it with cupcake cases. If you want to be particular, add about 1/4 of cup of mixture to each cupcake case.
Bake your cupcakes for 15-18 mins and then allow them to sit in the tin for about 30 mins until cool and then place them on a wire rack.
Set-up a double boiler (heat-resistant glass bowl on top of a pot of simmering water) and add to that the egg whites, sugar and salt. Whisk occasionally until either the mixture has reached 160 F or (like me if you didn't have a sugar thermometer) wait until the sugar has melted.
You won't really be able to tell when the sugar has melted but the meringue has to be HOT HOT HOT. Just about too hot to touch. Once you've reached that stage, throw into an electric mixer and put it on a low setting with the whisk attachment and whisk it until the bottom of the bowl is cool to the touch (10-15 mins).
Now turn it up to a higher speed and whisk the meringue till you get stiff peaks. Once you've got stiff peaks, add the butter a little at a time (about 2-3tbsps) allowing it to be completely mixed in before adding anymore. It might curdle at some point, this happens, just put the mixer on a high speed and it will eventually come together.
Once you're happy with your icing, add 2-3 tsps of peppermint, and colour it mint green. And then ice your cupcakes! Drizzle with chocolate sauce and shove a whole cupcake into your mouth/face.