Firstly, grease and line the bottom and sides of an 8-inch square baking pan with baking paper, then grease on top of the paper lightly. Make sure the baking paper drapes over at least two sides.
Then in a deep pan combine the sugar, golden syrup, 120ml water and bring to a boil over medium-high heat. Continue to boil until the caramel is a warm golden brown colour. Don’t stir – just swirl the pan every now and then to mix, being careful not to let it burn.
In the meantime bring the cream, butter, and sea salt flakes just to a simmer in a small pan over medium heat. Then remove from the heat, and set aside to keep warm until needed.
When the caramelised sugar is the right colour, slowly add the cream mixture to the caramel – be careful as it will boil up violently. Then stir in the vanilla with a wooden spoon and boil again over medium heat for 5 to 10 minutes, until the mixture reaches 120C on a candy thermometer. As soon as its reached 120C very carefully pour the caramel into the prepared pan and place in the fridge until firm.
Once cooled and firm, cut the caramel into small rectangles and wrap in baking paper.