In a microwave-safe bowl, combine the butter, brown sugar, and milk, stirring until the butter is melted and the mixture is well combined. The warmth from the butter will help dissolve the sugar slightly, creating a smoother dough base. This wet mixture forms the foundation for your cookie, so make sure everything is evenly incorporated before moving on.

In a small separate bowl, whisk together the flour, baking soda, salt, and vanilla extract. This pre-mixing ensures the leavening agent is evenly distributed throughout the dough, which is especially important in such a small batch. Add this dry mixture to the wet ingredients from Step 1 and stir until a cohesive dough forms with no visible streaks of flour.

Gently fold the chocolate chips into the dough from Step 2, distributing them evenly throughout. Transfer the dough onto a microwave-safe plate and flatten it into a circle about 1/4 inch thick—this thickness is crucial for even cooking in the microwave. I like to leave the edges slightly thicker than the center since they cook a bit faster in the microwave.

Microwave the cookie on high power for 1 minute. The cookie will continue to set as it cools, so remove it when it still looks slightly underdone in the center—it should be soft but not wet. Let it rest on the plate for 1 minute before eating; this allows the structure to set up properly and makes it easier to handle without the cookie falling apart.