Combine brown sugar, butter, sweetened condensed milk, golden syrup, vanilla, and salt into a saucepan
Cook on low heat, lower than you think, stirring occasionally. The low heat will prevent the sugar crystallizing and it is the crystallized sugar that makes fudge grainy.
Continue cooking until the color darkens and you can see the bottom of the pan when you stir
Remove from heat and stir in the white chocolate
Pour into an 8-inch square tin lined with baking paper
Press roasted macadamias into the fudge
Allow to set overnight
Slice and package
