Place the sugar in a medium saucepan over medium-high heat and stir constantly until it melts into an amber-colored liquid and no sugar clumps remain, 5-6 minutes.
Reduce the heat to medium. Carefully add the butter (it will bubble up when you do) and use a whisk to combine it with the sugar mixture until the butter is fully melted and incorporated, 2-3 minutes.
Add the heavy whipping cream in a steady stream while whisking. As soon as the cream is incorporated, let the caramel boil for a full minute before removing it from the heat and stirring in the salt.
Let the caramel cool to room temperature before using it in a cake recipe or as a drip. If you're using it to drizzle over ice cream or warm baked goods, you only need to cool it slightly (20 minutes or so). It will thicken as it cools.
