First, make the cupcakes. Preheat your oven to 350° degrees F. Line 2 muffin tins with approximately 14-16 cupcake liners. This recipe makes approximately 14-16 cupcakes.
In the bowl of a stand mixer, beat together the oil, milk, vanilla extract, and egg until combined; set aside. Meanwhile, in another medium bowl, combine the flour, sugar, cocoa powder, baking soda, and salt and whisk until combined. Gradually add in the dry mixture to the wet mixture, mixing on low speed until just barely combined (you should still see some dry mixture). Slowly and carefully stream in the hot brewed black coffee and mix on low speed until just combined and batter is thin and glossy. Batter will be very thin.
Divide batter among muffin tins, filling about 2/3 of the way full. Bake for 15-18 minutes or until a toothpick inserted near the center of the cupcake comes out clean or with moist, but not wet, crumbs. Cool the cupcakes completely.
Using a paring knife or a cupcake corer, core the cooled cupcakes and set the cores aside in a small bowl, Now we'll make the filling. In a medium bowl, combine the softened butter, confectioners' sugar, and marshmallow fluff and, using an electric mixer, beat on low speed until just combined. Spoon the filling into a piping bag or a Ziploc bag and snip off the tip. Pipe about a Tablespoon or two into the cavity of each cored cupcake. Replace the cupcake top (trim off most of the core as the cupcakes are now filled and we really only need the top of the cupcake back). Set aside.
For the ganache: Add the heavy whipping cream to a medium bowl and microwave on high power for 30 seconds or until hot to the touch. Add the chocolate chips to the bowl in a single layer. Replace the bowl back into the microwave to sit undisturbed for about 2 minutes. Remove from the microwave and stir until glossy and smooth and chips are all melted. Spread the ganache over the cupcakes or dip the cupcakes into the ganache and allow any excess to drip off. Allow ganache frosting to set before proceeding.
Lastly, for the vanilla icing piping garnish! In a medium bowl, combine the softened butter and confectioners' sugar and beat with an electric mixer until sandy and crumbly. Add in the heavy cream and splash of vanilla and mix until just barely combined into a frosting. Spoon the frosting into a small piping bag fitted with a Wilton #3 tip or Ziploc baggy and snip off the corner. Pipe a loop-de-loop pattern with steady pressure over the cupcakes. Think of piping a cursive 'e' over and over the cupcakes.
Cupcakes will last about 3-5 days airtight at room temperature or in the fridge. If in the fridge, serve cool but not cold.