In a small glass bowl, microwave chocolate chips and sweetened condensed milk on high one minute, then stir. Heat again for one minute and stir. Repeat until chips are melted and stir to mix well.
Pour into a bowl or 8x8 glass pan, spreading evenly.
Drop marshmallow fluff by Tbsp randomly over chocolate mixture.
Microwave on high about 30 seconds or until fluff is softened.
Using a butter knife, swirl the marshmallow fluff through the chocolate, creating a marbled appearance.
Serve immediately with graham crackers, cookies, pretzels, etc for dipping.
Store covered in the fridge for up to a week.
To reheat, place in microwave for 30 second increments until softened.