Pour corn syrup into the bottom of a 2 quart sauce pan and swirl to evenly cover the bottom. Add lemon juice and evenly sprinkle sugar over the bottom.

Place pan over medium low heat and cook without stirring for 5 minutes or until the corn syrup starts to bubble and the sugar on the surface starts to break apart.

Use the tip of a butter knife to gently tap and break up the large chunks of sugar.

Continue to cook another 2 minutes until sugar begins to melt. Gently stir using the tip of a butter knife. Mixture will clump up at first, but will melt with continued cooking.

Continue cooking slowly, stirring occasionally to prevent hot spots and evenly melt the sugar.

Once the syrup is clear and taking on an amber color and immediately after you see the first wisp of smoke rise from the surface of the caramel (after about 13 ½ minutes total), turn off the burner and remove the pan from the heat and carefully pour in the cold heavy cream. (Move quickly here to stop the cooking otherwise your caramel will quickly become too dark and bitter.)

Carefully stir with a long handled spoon or spatula. It will bubble up and get clumpy, but continue to stir and the caramel will melt back together.

Move pan back to the off but still warm burner and add vanilla extract, salt and butter and continue stirring until caramel is smooth and butter is melted and incorporated.

Transfer to a heat proof, sterilized container, let cool and cover tightly. Store in the refrigerator for up to 2 weeks.