In heavy medium saucepan stir together sugar, all-purpose flour, and salt. Gradually stir in half-and-half or light cream. Add vanilla bean, split lengthwise. Cook and stir over medium heat until thickened and bubbly. Cook and stir 1 minute more. Very gradually stir about half of hot mixture into egg yolks. Return egg yolk mixture to saucepan. Bring to gentle boil; reduce heat. Cook and stir 2 minutes more. Remove from heat. Remove and discard vanilla bean. (If desired, vanilla can be stirred in at this point to substitute for vanilla bean.) Cover with plastic wrap. To keep scum from forming, make sure plastic wrap lies directly on surface of mixture. Cool slightly, or chill in refrigerator until serving time. (Do not stir.) Makes 1 cup.