In a small bowl or mug, melt the butter halfway in the microwave. Take it out and stir with a spoon to fully melt it — we're going for a slightly thicker than 100% melted consistency.
Stir in the sugars, and pinch of salt. (At this point if you want to put it in the fridge for 5 minutes you'll get a better texture, but that's optional).
Add the splash of vanilla and the milk, and stir to combine. Gently stir in the flour, then the chocolate chips.
Enjoy!
Recipe by The Kitchen Paper at http://c02.ddd.mwp.accessdomain.com/single-serving-chocolate-chip-cookie-dough/