Measure out the cream in a jug and leave to one side.
Measure out the butter and cut into small cubes. Leave to one side.
Add the sugar and water to a large saucepan and pop onto a low/medium heat.
Stir continuously until the sugar has completely dissolved (the mixture will be cloudy)
Once the sugar has dissolved stop stirring and leave the mixture to come to the boil.
Once the mixture is boiling, leave until it turns a lovely amber colour, and then remove from the heat. This can take up to 10 minutes.
Whisk the caramel and add in the double cream. This will bubble and spit so please be careful. Keep whisking as quickly as you can until the bubbling has stopped.
Add in the butter and whisk again until it is completely melted.
Careful pour the mixture into a clean jar, pop the lid on and place it into the fridge until it is completely cool.