Prepare brownies according to box directions, but pour into heart shaped silicone mold (slightly overfill) or into lined cupcake tins.
Bake at 350 for approximately 30 minutes (until toothpick inserted in middle comes out clean).
Combine marshmallow cream, vanilla, powdered sugar and softened butter until blended to make filling.
Transfer to piping bag or to zippered bag to use for piping.
Remove top of each to make them flat and level.
Core out a hole in the middle of each, removing brownie.
Pipe in filling.
Melt chocolate chips by microwaving for 30 seconds and then stirring and repeating until melted and smooth.
Dip top of each cake in chocolate and place on rack to cool.
Place rack in refrigerator for 15 minutes.
Transfer remaining filling to a smaller bag and clip very small piece off end in order to write messages on cakes.