Melt butter in a microwave safe bowl for 20 seconds.
In mug, mix together sugar, cocoa powder, cinnamon, baking powder, beaten egg, milk, melted butter and flour with a fork until well blended. Add caramel pieces and chocolate chips.
Cook for 1 minute 10 seconds (1000 watts) or 1 minute 20 seconds (800 watts).
The cake will continue to cook when you remove it from the microwave, so even if the top seems soft it will set quickly.