LINE 8-inch-square baking pan with foil; grease.
COMBINE butter, granulated sugar, brown sugar and corn syrup in heavy-duty, medium saucepan. Cook over medium heat, stirring constantly, until mixture comes to a boil and butter is melted. Add sweetened condensed milk and Choco Bake. Cook over medium-low heat, stirring frequently, for 25 to 35 minutes or until mixture reaches 245° F on candy thermometer. Remove from heat; stir in vanilla extract. Immediately pour into prepared pan. Cool at room temperature. Makes about 2 1/2 pounds.
LIFT from pan; remove foil. Cut into about 1/2-inch squares or size desired and wrap individually in plastic wrap, twisting ends. Store in refrigerator or at room temperature; use within 7 to 10 days.