In a medium saucepan melt butter completely then add in the keto brown sugar and the sea salt whisking for the best sugar dissolve. Keep stirring and heating for 3-5 minutes until it turns from a sandy texture to a smooth texture

Now stir in the heavy whipping cream and whisk vigorously to incorporate it until smooth again. Let it heat up again until it comes to a boil and whisk it well. Turn the heat down to medium low and let it remain at a low boil.

Now is the time for patience as you need to bring the temperature of the butterscotch up to 225F which is slightly under the soft ball stage of 240F. This creates a smooth sauce that will not crystallize once cooled. It took about 15-20 minutes of a low boil for it to get to the 225F temperature.

You need a candy thermometer in order to measure the temperature as relying on the sauce coating a spoon is not as reliable. If you do not have a candy thermometer, you can just set your timer for the allotted 15-20 minutes total time and go from there.

At this point it will resemble a thick maple syrup consistency, but very hot. Remove it from the heat and whisk in the vanilla extract. It will bubble up a little, then turn smooth. Let it sit away from the heat and occasionally stir it for 10 minutes.

Now you can bottle it up or pour into an airtight jar or container. Keep in mind that it will thicken up considerably almost to a paste so make sure you can spoon it out of the container you choose. You can always warm it up to make it pourable by heating in a small saucepan, or placing the jar in a bowl of warm water. Some syrups are stored in plastic bottles, but it would be hard to squeeze out this butterscotch syrup once it is cold.

It will keep in the fridge up to 1 month, or frozen for 3 months. If you choose to freeze it, put dollops into an ice cube tray, or small scoops onto a parchment lined pan and freeze. Once it has frozen, remove the cubes and put into a freezer zip top bag. To use, warm up the cube in a pan over medium heat or add one directly to your hot cup of dark roast coffee.