Combine milk and cream in heavy medium saucepan. Scrape in seeds from vanilla bean; add bean. Bring milk mixture to simmer. Remove from heat.
Whisk egg yolks and sugar in medium bowl to blend. Gradually whisk hot milk mixture into yolk mixture. Return custard to saucepan. Stir over low heat until custard thickens and leaves path on back of spoon when finger is drawn across, about 5minutes (do not boil).
Strain sauce into bowl. Cover and chill. (Can be made 1 day ahead.)