Preheat oven to 350°F. Grease a 10 cast skillet pan with butter. Set it aside.
Cream together the softened butter, light brown sugar, and granulated sugar for 1-2 minutes until fluffy. Add in the eggs, vanilla extract, and peppermint extract and mix until combined.
To the bowl, add in the flour, cocoa powder, baking soda, salt, and espresso powder. Mix until the cookie dough forms. Then, fold in the chocolate chips.
Dump the cookie dough into the prepared skillet and spread it out evenly.
Bake for 30-33 minutes. The skillet cookie will still be slightly soft in the middle, but will firm up as the cookie cools. Allow it to cool for 15-20 minutes before enjoying. Enjoy as is, or top with crushed candy canes and/or vanilla ice cream!