2 cups sugar
2 cups heavy whipping cream, divided
1 3/4 cup light corn syrup
1 cup (2 sticks) unsalted butter
1 teaspoon vanilla extract
1/4 teaspoon salt
Place candy thermometer in a large, heavy-bottomed saucepan and grease a 9×13-inch baking dish with butter or butter-greased parchment paper.
Combine sugar, corn syrup and butter, plus 1/4 cup cream in saucepan over medium-high heat and bring to a boil, stirring continuously.
Once boiling (and continuing to stir), slowly pour in remaining heavy cream.
While stirring, monitor thermometer until it reaches soft-ball stage (236-240º F).
Optional: have a glass of cold water next to your workstation and when caramel approaches soft ball stage, take a spoonful and place it in cold water.
After 3-4 seconds, take caramel in your fingers; it should form a firm, soft ball, but should not be hard. It should still be malleable to the touch.
At this stage, caramel will turn transparent. Remove from heat and stir in vanilla extract and salt, if using.
Pour into prepared and greased dish, then let cool and cut into squares or rectangles. Optional: wrap in parchment paper.