Okay. So I made cupcakes this afternoon. It was my first experience filling cupcakes with stuff, so it was fun.
First I bought devil's food cupcake mix, and followed the box's instructions, adding just a little bit of black icing dye, then baked them. Once they were done, I let them cool, then used a cupcake corer (you could also use a knife, I just happened to have a corer) to pull out the center of the cupcake. Then I used a piping bag to fill the center with marshmallow cream filling.
Since I only made 12 cupcakes, I halved the recipe below for the filling:
Cream Filling (Enough to fill and decorate 24 cupcakes)
1 (7 oz) jar marshmallow cream
1/2 cup shortening
1/3 cup powdered sugar
1/2 tsp vanilla extract
Basically you just combine all of the ingredients, and whip them together until it's a sort of fluffy mixture.
After the cupcakes are filled, I took the top off of the cut out pieces of cupcake and put them back on over the filling. Then I iced them with chocolate frosting that also had black icing dye added.