In a large mug, melt the butter in the microwave, 15 to 30 seconds. Add the sugar and brown sugar; stir to combine. Add the egg and vanilla extract; whisk to combine.
Add the flour, baking powder and salt to the mug; stir to combine. Stir in the chocolate chips.
Put the mug in the microwave and cook for 1 to 2 minutes, or until a toothpick inserted into the center comes out clean. Serve immediately.