Preheat the oven to 350° fahrenheit (177° celcius)
Melt chocolate in a double boiler, watching carefully so that it does not burn.
With an electric or stand mixer, beat the butter and sugar.
Add the eggs, one at a time.
Beat at high speed for 5 minutes.
Add the vanilla, mint extract, and melted chocolate.
Stir in dry ingredients, alternating with the sour cream.
Stir in the boiling water. Batter will be thin.
Pour batter at once into the cupcake trays, only filling each cupcake liner less than ¾ of the way. You should have two dozen cupcakes with batter to spare.
Bake for 8-12 minutes, or just until pores form in the center of the cupcake top and the batter does not jiggle when you shake the tray. Be careful not to overbake though!