Cook corn syrup, sugar, and 1 cup warm water in a medium saucepan over high heat, stirring constantly, 3 minutes or until sugar dissolves. Using a pastry brush dipped in water, brush down any sugar crystals on sides of pan.
Bring to a boil; reduce heat to medium, and simmer, stirring occasionally, 23 minutes or until mixture turns pale amber. Remove pan from heat, and carefully stir in remaining 1/4 cup warm water. Stir in cream, butter, and vanilla.
Cook mixture over medium-low heat 5 to 6 minutes or until sauce thickens and a candy thermometer registers 220° to 222°.