Grease an 8x8-inch baking pan.
In a medium saucepan over medium-high heat, add the sugar, corn syrup, butter, and ¼ cup of cream.
Bring to a boil, stirring continuously.
While continuing to stir, add the remaining cream. Insert a candy thermometer and while constantly stirring, bring to the soft ball stage. Around 250°F, the sugar syrup will turn transparent and boil rapidly.
Around 320°F, the syrup will darken slightly and smell caramel-like. You can proceed to the next step any time after the syrup reaches 250°F and before it reaches 325°F.
Remove caramel from the heat and stir in the vanilla. Pour into the prepared baking pan.
While still warm, use a toothpick to pop any air bubbles that rise to the top. Allow cooling overnight.
Use a thin knife or small offset spatula to loosen the caramel block from the pan. Transfer the block to a cutting board and cut into desired size and shape. Wrap individually in wax paper if desired.