Grease and line a square 8x8 inch pan with baking paper.
In a glass microwave-safe bowl, heat the chocolate chips and heavy cream for one minute, then stir. Heat in 15-second intervals until the chocolate is fully melted and smooth.
Working quickly, add the vanilla extract and marshmallow fluff and stir until fully combined and smooth. Quickly pour the mixture into the prepared pan and smooth the top.
Refrigerate for one hour until firm. Slice into 16 squares. Store in the freezer in an airtight container.