Preparation - Place sugars, corn syrup, half and half and chocolate in a large saucepan. Bring to a boil over medium high heat until chocolate is melted and sugar is dissolved. Reduce heat to medium and cook, stirring occasionally, until mixture reaches 250° F on a candy thermometer (firm ball stage). Remove from heat. Stir in butter until it melts. Stir in vanilla. Pour into a buttered 8" x 8" x 2" pan. Cool, then cut cut into small squares. Wrap individual pieces in plastic wrap. Store in a cool, dry place.
