Line a 9" square pan with parchment paper, and for the easiest removal, you can also spread a bit of butter on top of the parchment. Set aside.
Add the butter, sugar, and corn syrup to a large heavy-bottom (at least 3 qt. size) pot. Bring it to a rolling boil over medium heat.
1 cup butter (2 sticks), 1 cup sugar, 1 cup light corn syrup (Karo)
While stirring or whisking, slowly add the sweetened condensed milk to the boiling mixture.
1 (14 ounce) can sweetened condensed milk (or 1 3/4 cup heavy cream)
Continue boiling over medium heat, stirring constantly, until it reaches soft ball stage (235 - 240℉). Use a candy thermometer to achieve the most accurate cooking time.
Remove from the heat, add the vanilla, stir to combine, and immediately pour the caramel into your parchment-lined pan.
1 tsp. vanilla extract
Let it cool for about 30 minutes, then sprinkle the top with coarse salt.
coarse salt or salt flakes (optional)
Cool completely. Refrigerating the caramel for at least an hour before cutting, helps to make it easier to work with.
With a long sharp knife, cut the caramel into little candy pieces and wrap them individually in parchment paper or candy papers. Store the wrapped candies in an airtight bag or container.