Place butter in an oversized microwave-safe mug. Melt in microwave for about 40 seconds (for cold butter) or until completely melted.
Add remaining ingredients except chocolate chips. Mix with a small whisk until dough comes together. Stir in chocolate chips.
Press dough evenly across the bottom of the mug. Or, if you want to make a traditional cookie, scoop the batter out of the mug and form it into a cookie shape (round thick disc) on a microwave-safe plate lined with parchment paper.
Cook in microwave for about 50 seconds. Let cookie cool a few minutes to firm up. Then eat immediately. Please note, cookie must be eaten immediately or it will dry out and harden after a while.
The nutrition information provided are only estimates based on an online nutritional calculator. This is not a comprehensive list of all the nutrients in the recipe (i.e., does not include vitamins, cholesterol, etc). I am not a certified nutritionist. Please consult a nutritionist or doctor for accurate information and any dietary restrictions and concerns you may have.