Combine all ingredients except caramel in an oversized coffee mug.
Whisk well with a fork until smooth. Microwave on high for 50 seconds. Cake should have started to turn solid form but still somewhat liquidy.
Remove cup from microwave and add in caramel to the center of the cake. Push it slightly down so that the chocolate batter covers the caramel, but you don't want to push it too far down as the caramel will sink while cooking. Cook for an additional 40 seconds and check if batter is done. If it is is still gooey, cook for an additional 30 seconds. Mine was done at 1 min 45 seconds (total cook time including 50 seconds before adding caramel sauce). Cool for a few minutes before serving while still warm.