I saw the Chocolate Pistachio Fudge on TV a couple of days ago, bought all the stuff and tried it last night. It didn't go so well for me though, as it is very soft. I did 2 lots, one with white chocolate, the other milk choc, and the white is runnier to the point it turns into a puddle when it defrosts. I have no idea what I could possibly have done wrong, twice?
Nigella's Chocolate Pistachio Fudge (from NIGELLA EXPRESS) is quick and easy to make. It is slightly softer than a boiled fudge so should be stored in the fridge, but once chilled it should be firm and not runny.
However we would highlight that the recipe is made with dark (bittersweet) chocolate with cocoa solids of 70%. This is important as the cocoa solids help the fudge to set. White chocolate does not contain any cocoa solids, it is mainly cocoa butter, sugar and milk and so it will not set when chilled. However you could use it as a sauce for ice cream. Milk chocolate also has a lower level of cocoa solids and a higher level of fat than dark chocolate, so it will set slightly more than white chocolate but will still not set as well as the dark chocolate version. If you are trying the fudge again then we would recommend using a good quality dark chocolate with 70% cocoa solids.