Combine half-and-half, 1/4 cup sugar, corn syrup, salt, and evaporated milk in a medium heavy saucepan. Scrape seeds from vanilla bean; add seeds and bean to milk mixture. Heat milk mixture to 180° or until tiny bubbles form around edge (do not boil). Remove pan from heat; cover and let stand 10 minutes. Combine remaining 1/4 cup sugar and egg yolks in a medium bowl, stirring well with a whisk. Gradually add hot milk mixture to egg mixture, stirring constantly with a whisk. Return milk mixture to pan. Cook over medium heat until a thermometer registers 160°, stirring constantly. Remove from heat. Place pan in a large ice-filled bowl for 20 minutes or until egg mixture is cool, stirring occasionally. Pour milk mixture through a fine sieve into the freezer can of an ice-cream freezer; discard solids. Freeze according to manufacturer's instructions. Spoon ice cream into a freezer-safe container; cover and freeze 3 hours or until firm.