Prepare and bake cupcakes according to package instructions, using paper-lined muffin cups. Cool for 5 minutes before removing to wire racks to cool completely.
Filling: In a small bowl, combine water and salt until salt is dissolved - cool. In a small mixing bowl, beat the marshmallow creme, shortening, powdered sugar and vanilla on high until light and fluffy; Add the salt mixture.
Insert a small round pastry tip into a pastry or plastic bag; fill with cream filling; Insert the tip halfway into center of each cupcake and squeeze in small amount.
Frosting: In a heavy sauce pan, melt the chocolate chips with cream. Cool. Dip cupcake tops into frosting; chill for 20 minutes; store in refrigerator.
Garnish with sprinkles and white frosting (if desired).
