Line an 8×8 inch pan with parchment paper and lightly butter it.
In a heavy saucepan, melt butter over medium heat.
Add sugar, corn syrup, and condensed milk; stir until fully combined.
Cook over medium heat, stirring constantly, until mixture reaches 245°F (firm-ball stage).
Remove from heat and stir in vanilla extract and sea salt.
Pour the caramel into the prepared pan and spread evenly.
Allow to cool at room temperature for 2–3 hours or until firm.
Cut into squares and wrap individually in wax paper.
