Add the granulated white sugar to a large sauce pan and heat it over medium-low heat. As the sugar is heating it will crystalize and then eventually all melt down and turn golden in color. When most of the sugar has melted, but there are still a few crystalized clumps, turn the heat down to low so the melted sugar doesn't burn. (Melting all the sugar takes around 20 minutes.)
1 cup (200 g) granulated white sugar
Once all the sugar has melted and turned golden in color, add in the butter right away. Stir quickly until the butter is incorporated.
5 tbsp (70 g) salted butter, softened
Then add in the heavy cream and stir quickly again to incorporate everything together. (At this point if you see the butter and cream start to separate from the sugar turn the heat up to medium low and stir vigorously to combine everything together. This can happen if your butter and cream aren't room temperature.)
1/2 cup (120 ml) heavy cream, at room temperature
Lastly, add in the sea salt and vanilla and stir to combine.
1 tsp vanilla, 1/4-1/2 tsp salt
Let the caramel simmer on low for 2-3 minutes, then remove it from the heat and allow to cool completely before using.