In heavy saucepan combine half-and-half, 3/4 cup sugar, and vanilla bean and bring just to a boil. Remove pan from heat. in a bowl whisk together egg yolks and remaining 1/4 cup sugar and hot half-and-half mixture in a stream, whisking. Return custard to pan and cook over moderately low heat, stirring, until 170ºF on a candy thermometer.
