Add brown sugar and water in a sauce pan over medium low heat.
When the sugar is melted, add in the butter.
When the butter is melted, pour in the heavy cream and whisk it well.
Now increase the heat and bring it to a boil.
Boil for 2 - 3 minutes whisking constantly making sure it doesn't burn and then take it off the heat. Be careful as it boils quite vigorously.
Stir for few minutes until the bubbling stops and the mixture is smooth. Now add the vanilla extract and sea salt or fleur de sel and mix.
Let the caramel cool for 20-25 minutes and then serve with your favourite ice cream or cake or dessert.
Or store it in an airtight glass container and refrigerate. Reheat to serve.