
Combine all cake ingredients in a mug except for chopped apple. Stir until well-combined then stir in apple.
In a small mixing bowl, combine salted caramel sauce ingredients and stir to combine.
Place both mug and bowl in microwave and cook on full power 2 minutes, checking cake for doneness around 90 seconds. Cake is done when top appears set and springs back a bit when you touch the surface.
When cake is done, remove from microwave and cook caramel another 1-1/2 minutes (a total of 3 minutes) or until bubbling, emulsified, and thickened. Carefully remove from microwave (bowl will be hot) and pour over apple cake. Let cool slightly then enjoy!