Add sugar to a heavy sauce pan on med-high.
Allow sugar to melt then start to whisk as sugar melts.
Lower heat to med when sugar has melted and turn amber colour.
Add in butter one by by and whisk as you do it, it will bubble up quite vigorously.
Pour in heavy cream while whisking.
When combined remove from heat, stir in salt and vanilla extract.
Allow to cool for 20 mins before pouring into air-tight glass jar.
Store in fridge for up to 2 weeks.