Lightly grease and line a 20cm (8in) square tin with nonstick baking paper.
Put the sugars, glucose syrup, double cream, butter and vanilla pod into a saucepan and place over a low heat. Stir constantly for about 10 minutes or until the sugar has dissolved. Turn up the heat slightly and simmer for about 15 minutes or until it reaches 113-118ºC on a cook’s thermometer. If you do not have a thermometer, drop a little of the mixture into cold water and if it forms a ball, the fudge is ready.
Take the pan off the heat, pour the mixture into a large bowl, remove the vanilla pod and leave to cool for 10 minutes. Then add the icing sugar and beat vigorously with a wooden spoon for about 3-4 minutes.
Spoon into the tin, smooth the surface and then sprinkle with a little sea salt. Leave to cool, chill until set (ideally overnight) and then cut into squares and pack into boxes and tie up with ribbon. Keep in the fridge until needed.