Step 1

Add the butter to a large mug and microwave until melted.

Step 2

Remove from the microwave and whisk in the brown sugar (I use a fork for this).

Step 3

Ensure that the butter isn't too hot (otherwise, you'll scramble the egg), then whisk in the egg yolk and vanilla extract.

Step 4

Stir in the flour (the mixture should be thick like cookie dough), then stir in the chocolate chips.

Step 5

Microwave on medium power (50-70%) for 60-90 seconds or until the top looks just set. Do not microwave on high power, otherwise, the cookie can become hard and the chocolate can burn. I check after 60 seconds to see, then add an extra 15 seconds as needed.

Step 6

Enjoy immediately, optionally with a scoop of ice cream.