Preheat oven to 350 degrees Fahrenheit. Line the cookie sheet with parchment paper, baking mat, or use oil.

In a large bowl, add butter, sugars and mix until well combined. Add egg, vanilla extract, and continue mixing.

In another bowl add cocoa powder, salt, baking soda, and mix until well combined. Add dry ingredients to wet ingredients and mix.

Roll cookies into 1 inch balls and bake for 10-12 minutes.