Heat a thick bottomed pan over medium heat, add the butter whisking frequently.
Once the butter is melted it will foam up, then the foam should start to go away. Watch carefully as lightly browned specks begin to form at the bottom of the pan.
As soon as you notice the browned specks in the butter, remove from the heat and whisk in the sugar substitute. Continue whisking until the sugar substitute has completely melted.
Return to medium-low heat and slowly whisk in the heavy cream and vanilla. Bring to a low boil, whisking constantly
Reduce heat to low and allow the mixture to simmer, whisking frequently, until it coats the back of a spoon. This will probably take about 10 minutes, but be sure to watch closely and stir frequently to prevent burning.
Once it has thickened, remove from the heat and allow it to cool slightly in the pan, continuing to whisk frequently until it reaches the desired serving temperature. At this time you can stir in the salt, or sprinkle it on top when serving.
Nutrition info for 1 serving (approximately 1 ½ tbsp) - 94 calories, 10g fat, 0g carbohydrates, 0g protein This nutrition information is only an estimate and will vary based upon yield and exact ingredients used.