Set out all your ingredients before you begin. They don't need to come to room temperature first, but if they sit out for a few minutes before you start, that's ok too.

Add the sugar to a medium saucepan (a nonstick works great). Cook the sugar on medium heat, stirring lazily. For the first few minutes, it will seem like nothing is happening but eventually the sugar will begin to break down. After a few minutes, the sugar will melt into a coppery-caramely-colored liquid. Make sure all the little chunks of sugar are gone! If the sugar isn't completely liquified, the caramel sauce won't turn out.

Once the sugar has completely melted, immediately add the butter and reduce the heat slightly. Whisk or stir constantly until the butter is completely melted. If the butter separates a little from the caramel, don't worry. Whisk it in as best you can, and continue to the next step.

Remove pan from the heat and slowly add the heavy cream, whisking as you add it. The caramel will bubble up here and some of it may harden from coming into contact with the cold cream - this is ok!

Set the pot back on the heat for about a minute more, stirring constantly, to let any hardened bits melt back down, and to let it thicken a bit. Remove from the heat, and add a pinch of flaky sea salt, to taste. Let cool 10-15 minutes before using.

Store cooled caramel in an airtight container in the fridge for up to 1 month. When using it out of the fridge, microwave it for about 30 seconds to soften it back up, so it's pourable.