Add chocolate chips and condensed milk to a medium microwave safe mixing bowl. Heat in microwave on HIGH power, in 30 second increments, stirring between intervals, until melted and smooth (at this point I thinned mine out with a few tablespoons of hot water so it wasn't so thick and so it stayed a nice dip-able consistency longer). Pour into a wide and shallow serving bowl or pie plate.
Dollop tablespoons of the marshmallow fluff over chocolate mixture, heat in microwave about 20 seconds longer until marshmallow has melted, then remove and using a sharp knife, swirl marshmallow into dip. (Alternately you can scoop marshmallow cream into a small microwave safe bowl and heat until it melts, about 15 - 20 seconds, then stir and scoop small spoonfuls randomly over top of chocolate mixture and swirl). Serve with graham crackers and optional strawberries.
Notes
Regular marshmallows can't be substituted for the marshmallow fluff. If you can't find marshmallow fluff at the store, you can easily make it yourself.