Put the sugar into a heavy based saucepan and pour the water over it. Cook over a low-medium heat to allow the sugar to dissolve (5-10 minutes)
Meanwhile, cube the butter
Once the sugar has dissolved, turn the heat to medium and allow the caramel to continue to cook until it reaches a rich amber colour - another 5-10 minutes (but be careful not to let the caramel burn and turn bitter)
Take off the heat and add 1/3 of the butter, mixing with a mini balloon whisk - it will rise and splutter a little, so be careful. Add another 1/3 butter, mix and then add the remaining butter. Mix again
Pour in the cream, vanilla extract and the salt (either 1/4 tsp or 3/4 tsp depending on your preference for regular caramel or salted caramel). Mix
Add the chocolate and beat with the balloon whisk until melted
Pass the caramel through a metal sieve, using a metal spoon to push the sauce through. This will ensure the caramel spread is lump free
Decant into small jars, let cool, then seal and store in the fridge
Let sit for 20 minutes before using
If the caramel cooks for too long, there is a chance the caramel will be too stiff to spread. If so, heat in the microwave on a low setting in short 10-second bursts until a spreading consistency is reached. Do not blast it at full power, else the spread will return to liquid form.
Alternatively, reheat the entire batch gently, to melt, and stir through a little extra cream - 1 or 2 tbsp, depending on how thick the spread is - then let it reset.