1. Grease one 8×8-inch square tin and set aside.
2. In a heavy saucepan over a medium flame, combine the confectioners’ sugar, milk, and margarine. Mix well and stir constantly until candy thermometer reads 238°F (112°C).
3. Remove from heat and add the chocolate, marshmallow fluff, vanilla, and cocoa. Stir together until all the chocolate and fluff is melted and distributed throughout the mixture.
4. Pour into prepared pan. Cool and serve. To store, refrigerate in an airtight container.
5. To serve as pictured, brush the tops of some of your squares with melted chocolate and garnish with chocolate shavings.