Combine dark brown soft sugar, caster sugar, butter, golden syrup, cream, milk and vanilla in a medium saucepan over medium heat. Heat, stirring occasionally, to 121 to 129 degrees C, or until a small amount of syrup dropped into cold water forms a rigid ball. Pour into a 20x20cm tin. Let cool before cutting into small squares.
I can only rate this from my experience - a total disaster. First it wouldn't go any higher than 102 degrees using two thermometers in case one wasn't working. Then, when I turned the heat up, it boiled over my cooker from the 'medium' sized saucepan I used. I then put it in two saucepans and, as soon as it got to temp, it burnt. Totally ruined. Sorry but I won't be using this recipe again. - 16 Dec 2012