Preheat the oven to 375°
Prepare baking sheets with parchment paper if desired.
In the large bowl of a mixer, add butter and mix until smooth.
Add in the sugar and beat until smooth and fluffy and the sugar isn't so gritty.
On low speed add in the egg, heavy cream, and vanilla.
Add the flour and cocoa and mix on medium until well combined.
Add a large star piping tip to a piping bag I used a #864 piping tip. Fill the piping bag 1/2 full (don't overfill the bag or it will be hard to pipe the cookie dough).
You'll start by piping the ears, two short bursts of dough in an open "V" shape. Then you'll add a large swirl on top of the ears.
Bake at 375° 8-10 minutes. The cookies should feel baked, so they won't be chewy when cooled. Butter cookies often have a slight "snap" to them once completely cooled.
Allow cookies to cool completely.
Mix icing and separate it with a very small portion for black and a large portion for white. Use food coloring to achieve the desired colors. I used black and white food coloring.
Place each color into piping bags, pipe on the ears, eyes, and mouth, then let the icing dry until firm. I kept the design simple, add more detail for the nose if desired.
Alternatively, you can use white and dark chocolate melted in a piping bag if desired.