Preheat the oven to 350°F. Line standard size muffin tins with cupcake liners and set aside.

In a large mixing bowl, combine the chocolate cake ingredients: cake mix, butter, eggs, sour cream, milk and vanilla extract. Beat on low speed for 1 minute and then on medium-high speed for two additional minutes.

Fill cupcake liners about halfway full.

Bake for 15 minutes and then cool completely.

Meanwhile, prepare the frosting. Chop the chocolate baking bar into small pieces. Use a double boiler or 30-second increments in the microwave to melt the chocolate. Stir until fully melted and set aside to cool (chocolate should not cool long enough to re-harden, just cool down so that it is not hot to the touch.)

Use a whisk to stir together the cocoa powder and hot water (or hot cream) until smooth and shiny.

In a large mixing bowl, beat together the softened butter, cooled chocolate bar, cocoa powder mixture, and powdered sugar. Beat until fully combined and fluffy.

Fill a piping bag with the prepared frosting and fit with piping tip #1M (or an open star piping tip). Pipe swirls of frosting to top each cupcake.

To make a bat topper, cut an Oreo cookie in half - a swift, strong chop with a sharp knife works best for a clean cut.

Separate the cookie from the cream filling.

Place two Oreo halves side by side to form the “wings” of the bat.

Twist one half from a mini Oreo. Using the half that still has the cream filling on it, press the mini Oreo over the center point where the “bat wings” meet. The cream filling will serve as the glue to hold the bat together.

Use a toothpick or small piping tip to dab two dots of frosting on the mini Oreo “bat face.”

Place two candy eyeballs on the dots of frosting.

Carefully place each assembled bat onto the top of a frosted cupcake.