Bring heavy cream to a simmer and turn off heat. Set aside.
Combine butter and sugar in a medium size heavy bottom pot on medium heat. Do NOT use a small sauce pan, otherwise you will have a mess when the heavy cream goes into the hot sugar.
Allow butter and sugar to melt, stirring often. If sugar granules stick to the sides of the pot, wet a pastry brush with water and gently push the sugar down into the bottom of the pot. This may need to be done repeatedly until the sugar is fully melted.
The sugar and butter will look somewhat grainy for about 5-7 minutes, but eventually the sugar will start to turn amber and will begin to look smooth.
Once the sugar and butter mixture is a deep amber or almond color, remove from heat and the cream 1 tablespoon at a time, whisking vigorously with each addition. After adding about half of the cream, add the remaining cream all at once and stir (the sauce will look thin).
To finish, add the salt. Stir until combined, and then transfer to a heat-proof container, preferably glass.
Refrigerate the caramel sauce for up to 3 weeks. This sauce is thicker once chilled, so place it in the microwave for 15-30 seconds to loosen it up.
