Preheat oven to 180C. Roast cashews on an oven tray, stirring occasionally, until golden and well-roasted (10-20 minutes).
Meanwhile, bring condensed milk, butter, golden syrup and ½ tsp salt to the simmer in a non-stick saucepan over high heat. Sift cocoa over and stir to combine, then simmer, stirring continuously, until fudge is very thick and a teaspoon of mixture forms a soft ball when dropped into cold water (10-15 minutes).
Stir in cashews and vanilla, then pour into a 20cm x 8cm loaf tin lined with baking paper and press the mixture flat with the back of an oiled spoon. Refrigerate until cool and set (30-45 minutes), then cut into 2cm pieces and serve. Fudge will keep in an airtight container for 7 days.
This recipe is from the September 2011 issue of Australian Gourmet Traveller.