In a heavy-bottomed saucepan over medium heat, heat the sugar. Stir constantly with a heat-resistant rubber spatula.
The sugar will clump, but it will eventually melt. Keep stirring until the sugar melts into a light brown liquid, about 3-4 minutes.
Once the sugar melts, immediately add in butter and vanilla bean seeds (if using). Stir constantly until butter is melted, about 1-2 minutes.
Slowly pour in heavy cream while stirring constantly. Continue stirring until the mixture comes up to a boil. Keep stirring and boil for 1 minute.
Remove pan from heat and add salt, stirring until combined.
Let the sauce cool for 10 minutes, then pour it into a glass jar.
Cool completely with the lid open, then cover and store in the refrigerator. The salted caramel sauce will thicken as it cools.
Notes
With this salted caramel recipe, you must constantly stir the entire time it's on the stovetop. It only takes 7 minutes, so put down your phone and make sure the kids are occupied for those 7 minutes. Keep the mixture moving because it can burn quickly!
If you use unsalted butter, add ¾ teaspoons of salt to the caramel sauce in step 5. Add ½ teaspoon of salt to the caramel sauce in step 5 if you use salted butter.
The vanilla bean seeds are optional, but I love using them because they enhance the luscious caramel flavor! You can also use ½ teaspoon of vanilla bean paste instead of the seeds.
I don't recommend doubling this recipe. I've tried it a few times, and the sugar doesn't melt properly, leaving sugar shards in the sauce—not ideal!
I make back-to-back batches when I want to make a lot of salted caramel sauce for gifting or other purposes.