Preheat the oven to 350 degrees F. and line a cupcake pan with liners.
Sift together the flour, cocoa powder, baking powder, baking soda, and salt. Add the bran from the flour back in.
In the bowl of a stand mixer, beat the butter and sugar together until well combined.
Add in the eggs and vanilla and mix.
Add the sour cream and milk and mix.
Add the sifted flour and cocoa and mix until combined.
Scoop into the prepared cupcake liners, filling them up about ¾ of the way to the top.
Bake for 15-20 minutes or until a toothpick inserted in the middle comes out clean.
Prepare the ganache filling by heating the heavy cream on medium heat in a saucepan until it gets hot. You do not want it to boil. Remove from the heat and fold in the chocolate chips. Set aside.
For the buttercream, beat the butter until it is whipped.
Sift the powdered sugar and cocoa powder together and add to the butter. Beat until fluffy.
Add the milk and vanilla and beat until light and fluffy.
Once the cupcakes have cooled, take a spoon and remove some of the cake from the center of the cupcake, about 2 tablespoons worth of cake.
Spoon in about 2 tablespoons of the ganache filling in them and top with the chocolate buttercream.
Top with a mini marshmallow if desired.