Place the whipping cream in a saucepan with the grated fresh ginger. Bring the cream to the boil and stir to make sure it doesn't burn on the bottom.
Turn off the heat and leave the cream to infuse with the ginger and cool to room temperature. When the cream has cooled, strain it into a bowl or a jug, making sure all of the ginger has been removed.
Add half the sugar to a heavy based saucepan and allow the sugar to melt on a medium heat, Add the rest of the sugar and heat it until it melts and becomes an amber caramel colour.
Reduce the heat to low and slowly add the cream, it will bubble up and steam will escape, so be careful not to burn yourself on the steam.
When all the cream has been added stir the caramel to evenly mix in the cream. Then add the salt and mix evenly.
Finally add the butter and stir until it has all melted, transfer the caramel to a bowl to cool and cover with a layer of clingfilm, make sure the clingfilm touches the surface of the caramel so that you don't get any condensation.