Line a 9x13-inch jelly pan with parchment paper, ensuring the paper fits the bottom and sides. Coat the parchment thoroughly with some softened butter so the caramels release easily after cooling.

In a large heavy-bottomed saucepan or pot, melt the butter over medium heat until fully liquefied.

In a medium bowl, mix together the light brown sugar, 1/4 teaspoon of coarse sea salt, light corn syrup, and sweetened condensed milk until well blended. Then, add this sugar mixture to the melted butter in the large pot on the stove.

Increase the heat to medium-high and cook, stirring occasionally, until the mixture begins to boil (about 10-15 minutes). Once boiling, reduce heat to medium, attach a candy thermometer to the pot, and cook while stirring constantly until the mixture reaches the Firm Ball Stage (245–248°F). This can take 20-30 minutes. The caramel should become thick, paste-like, and develop a deep hue. I always make sure to stir constantly during this step to keep the mixture from scorching.

Once the caramel reaches 245–248°F and is thick and dark, remove the pot from the heat. Carefully stir in the vanilla paste—it will bubble rapidly, so be cautious. Immediately pour the hot caramel into the prepared pan, spreading it evenly.

Allow the warm caramel to cool in the pan for 20–30 minutes, then sprinkle the remaining coarse sea salt evenly over the surface for a beautiful finish. Let the caramel cool completely at room temperature, ideally overnight, so it can firm up perfectly. I always let my caramels sit undisturbed overnight for the best texture.

Carefully lift the cooled caramel slab from the pan using the parchment paper, then place it on a large cutting board. Cut the caramel into 1x1-inch squares using a sharp knife or pizza cutter, and wrap each piece in wax candy wrappers to serve or gift.