Step 1

Spray a large microwave-safe mug with nonstick spray. Set aside.

Step 2

In a small bowl, mix the melted butter, sugars, egg yolk, and vanilla extract together.

Step 3

Stir in the flour, salt, and almost all of the chocolate chips (leave a few to sprinkle on top of the raw batter). Mix well.

Step 4

Use a spatula to transfer the dough to the prepared mug.

Step 5

Sprinkle the remaining chocolate chips on top of the dough.

Step 6

Microwave on high for 1 minute. The top of the cookie will look set and slightly puffed when done.

Step 7

Carefully remove the mug from the microwave and let it cool for a few minutes before enjoying. Serve with a scoop of vanilla ice cream, if desired.