In a heavy based pan mix together sugar and water. Melt sugar over medium heat stirring until the sugar has dissolved.
Turn up the heat to medium-high and leave to bubble for 4- 5 minutes until mixture turns to caramel.
Immediately remove from heat, then carefully stir in butter and cream. Caramel will bubble rapidly.
Stir in sea salt.
Leave the salted caramel sauce to cool, then transfer to an airtight container or jar.