In a heavy bottomed sauce pan, heat up the sugar on a low and steady heat. After a couple of minutes, you will notice that the sugar gets lumpy. (Step 1 and 2)
Keep stirring the sugar until it melts completely and wait for it to turn amber or slightly dark brown (dont let it turn too dark, the sugar will be burnt and bitter). This is one of the crucial steps as this gives the colour of the caramel (Step 3).
Add the butter cubes into the melted sugar syrup and give it a good swirl. (Be careful with this step and the next, as sugar might splutter and its HOT!!!) its not fun trust me... (Step 4)
Turn off the heat and add the cold heavy cream, this boils and splutters even more as the heavy cream is very cold.
Give a nice swirl until its all mixed and add the sea salt and give it a good mix.
Voila your salted caramel is done.