Step 1

Add butter to a 6 or 8-oz mug. Microwave until melted.

Step 2

Stir in sugars, salt, egg yolk, and vanilla. Then stir in flour, followed by the chocolate chips.

Step 3

Microwave for 1 minute at 80% power until top springs back. Color will be light.

Step 4

Serve with ice cream or whipped cream, if desired, and enjoy!