Prepare cupcakes according to package adding in the instant coffee along with the mix.
(alternatively) you could replace the liquid in the cake mix with cooled coffee, but the cupcakes won't have a white look to them.
Beat butter and sugar along with cream, mint and coffee, until smooth.
Pipe icing on cooled cupcakes with a #809 tip.
Place a piece of peppermint patty on top and dust with some instant coffee.