Generously spray the crock with cooking spray
In medium bowl sift together flour, cocoa mix, cocoa, and baking powder
In large bowl mix together sugar, butter, egg, vanilla and salt
Add the flour mixture to the egg mixture and carefully stir until smooth but don't overmix
Carefully spread the batter evenly into the crock (it will be pretty thick)
Spoon the marshmallow creme over the batter then run a knife through to swirl it all together
Sprinkle mini chocolate chips over the top
Cook on high for about 3 hours until the edges start to harden and the center starts to set
Let sit for an hour to cool, then cut into bars (if you can wait that long!)