Add the butter, water, vanilla, and salt to the microwave-safe coffee mug; stir the ingredients to combine them.
Mix in the cocoa powder, sugar, and flour.
Microwave the mixture for 30 seconds. Remove the coffee cup from microwave and pour the chocolate chips into the center.
Microwave for 30-45 seconds or until the cake looks slightly moist. The center should be slightly melted. Be careful not to overcook the cake.
Serve immediately. Enjoy!