Line an 8x8-inch baking pan with parchment paper, leaving some extra hanging over the sides so you can easily lift the fudge out later.

In a medium saucepan over low heat, add the chocolate chips, sweetened condensed milk, and butter. Stir constantly until the mixture is fully melted and smooth.

Remove the pan from the heat and stir in the vanilla extract until combined.

Pour the chocolate mixture into the prepared pan, spreading it evenly.

Spoon the caramel sauce over the top in small dollops, then use a knife or skewer to gently swirl it through the fudge. Sprinkle a bit of sea salt on top.

Place the pan in the refrigerator for 3-4 hours, or until the fudge is firm. Once set, lift it out using the parchment overhang and cut into squares.

Serve and enjoy, or store in an airtight container in the refrigerator.