Use 1 cake mix, according to directions.

 Filling:
1  8 oz cream cheese
1/3 cup sugar
1 egg
1  6 oz semisweet pieces
Beat until smooth.
 

Fill tins 2/3 full of batter, drop heaping teaspoon of filling on top of each cupcake.  Bake 15 to 20 minutes at 350 degree.