Cut the chocolate up finely. Line a 8x8 inch baking pan with baking paper.
Combine the sweetened condensed milk, sugar, corn syrup, golden syrup and butter in a heavy based saucepan. Stir, without boiling, until the sugar is dissolved.
Bring the mixture to a gentle simmer and, once it continues to bubble while you stir, simmer and stir for another 6-8 minutes. You should notice it thicken slightly.
Take the mixture off the heat and mix through the white chocolate and most of the salt (reserve a couple of pinches for topping), until fully incorporated and the mixture is smooth.
Pour the mixture into the lined baking tin. Sprinkle the remaining salt evenly over the top.
Leave for 30 minutes to cool at room temperature, then cover with plastic wrap and refrigerate overnight.
Cut into 36 squares and serve.