Line an 8×8-inch pan with parchment paper and set aside.
In a large saucepan place the condensed milk, sugar, butter, golden syrup/corn syrup and salt. Heat gently on low heat, stirring until all the sugar has dissolved. Continue stirring the fudge constantly on low or low-medium heat until it’s simmering and has thickened and coats the back of a spatula/spoon – this will take about 3-5 minutes.
Once the fudge has thickened, remove it from the heat. Add the white chocolate and whisk until all the chocolate has melted.
Transfer the fudge mixture into prepared pan. Allow the fudge to cool slightly at room temperature, then cover the pan and leave it to set in the fridge for at least 4 hours.
Once the fudge has set, cut it up in pieces and serve.
Fudge will keep in the fridge for up to 2 weeks. Serve it cold or at room temperature.
Notes
Cut the fudge into small pieces as it is very rich.