In a medium heavy-duty stainless steel saucepan (do not use nonstick) over medium heat, cook the sugar, stirring constantly with a wooden spoon or heat-safe silicone spatula. Sugar will form clumps and eventually melt into a thick brown, amber-colored liquid as you continue to stir. On my stove, this takes about 6 minutes. Stir constantly, especially around the bottom edges, and be careful not to let it burn.

Once the sugar is completely melted, reduce the heat to low and stir in the butter. Be careful in this step because the caramel will bubble rapidly when the butter is added. (If you’re nervous for splatter, wear kitchen gloves.) Cook and stir constantly until the butter is melted and well combined. If you notice the butter separating or if the sugar clumps up, remove the pan from heat and vigorously whisk to combine it again. Keep whisking until it comes back together, even if it takes 3–4 minutes. It will eventually—just keep whisking. Return to heat when it’s combined again.

Very slowly and carefully pour in the heavy cream, stirring constantly. Since the heavy cream is colder than the hot caramel, the mixture will rapidly bubble and steam when added. When all of the heavy cream has been added, stop stirring, increase the heat to medium, and let it boil for 1 minute. It will rise in the pan as it boils. If you’d like to be precise and use a candy thermometer, the temperature should reach 220°F (104°C).

Remove from heat and stir in the salt. The caramel will be a thin liquid at this point. Allow to slightly cool and thicken before using. Caramel thickens considerably as it cools.

Cover tightly and store in the refrigerator for up to 1 month. Caramel solidifies in the refrigerator. Reheat in the microwave or on the stove to desired consistency.