Scald half and half in heavy medium saucepan. Beat yolks and sugar in medium bowl to blend. Gradually whisk in hot half and half. Return to saucepan. Stir over medium-low heat until mixture thickens and leaves path on back of spoon when finger is drawn across, about 3 minutes; do not boil. Strain into medium bowl. Cool slightly. Stir in poire Williams and vanilla. Cover with plastic and refrigerate until well chilled. Creme Anglaise can be prepared 2 days ahead.)