Firstly, line a 8x8inch baking tin and set to one side.
Place the sugar, cream, butter and glucose into a large heavy-bottomed sauce pan, and place over a low heat. Stir constantly until the butter and sugar have melted - this will take about 5 minutes and the mixture will feel thinner and look pale yellow in colour.
Increase the heat slightly and bring to a very soft rolling boil, stirring all the time. Keep cooking until the mixture reaches 116C on a food thermometer. This will take around 25 minutes and the mixture will be thick, have reduced slightly and be a faint caramel colour. Take off the heat and leave to cool for 5 minutes, until its reduced in temperature to 110C.
Whilst the mixture is cooling, chop 50g of the chocolate roughly. Then stir into the cooled mixture with the salt, until fully combined.
Pour the mixture into a large heat proof bowl and either, using an electric hand whisk or a stand mixer, beat on a high speed until the mixture has cooled to around 60C. This should take around 10 minutes and it'll be quite thick. Then pour into your lined tin, level out carefully and then cover and leave to set overnight.
The next day, cut into 3x3cm squares to make 36 pieces of fudge. Then melt the remaining 50g of chocolate and drizzle over each fudge piece. Leave to set, and then store in air-tight containers or bags.
Will keep for 2-3 weeks in air-tight containers of boxes.