Melt the Sugar:
 In a medium, heavy-bottomed stainless steel saucepan (avoid nonstick), heat the sugar over medium heat. Stir continuously with a heat-resistant silicone spatula or wooden spoon. The sugar will clump at first but will gradually melt into a smooth amber liquid. This process typically takes 7-10 minutes, depending on your stove. Be careful not to let it burn.

Incorporate the Butter:
 Once the sugar is fully melted, carefully add the butter. Expect the mixture to bubble vigorously. Stir until the butter is fully melted and incorporated. If the mixture looks like it's separating or clumping, remove the pan from the heat and whisk vigorously until smooth (this may take 3-4 minutes). Once combined, return the saucepan to the heat.

Add the Cream:
 Slowly pour the room-temperature heavy cream into the caramel while stirring constantly. Be cautious, as the caramel will bubble up rapidly when the cream is added. Let the mixture boil for about 1 minute without stirring, allowing it to rise in the pan. If using a candy thermometer, the temperature should reach approximately 220°F (104°C).

Add Salt & Cool: 
Remove the caramel from the heat and stir in the salt. At this point, the caramel will be thin, but it will thicken as it cools. Let it cool slightly before using.

Storage:
Store in an airtight container in the refrigerator for up to 1 month. The caramel will solidify when cold; reheat gently in the microwave or on the stove until it reaches your desired consistency.