Place butter in a microwave-safe mug and melt in the microwave (about 20 seconds.)
Stir in white and brown sugars and vanilla extract.
Separate egg yolk from egg white and just add the egg yolk to the mug (discard remaining egg white or refrigerate it in an airtight container to use for later.)
Stir well, then add all-purpose flour.
Stir again and then add chocolate chips and stir one final time to combine.
Put the mug in the microwave and cook for approximately 40 seconds. Allow to cool then enjoy!
Video
Notes
If you only have unsalted butter to use, just add in a pinch of salt to this recipe.
Cookie will continue to cook when you take it out. Let it cool slightly then dig in! Or better yet, add a little ice cream on top!
No baking soda or baking powder is needed.
Also, there is enough butter in this recipe to keep it from sticking to the inside of the mug so nonstick spray isn't needed.
This can also be made in a ramekin or small microwave-safe bowl.