Place half and half in heavy medium saucepan. Scrape in seeds from vanilla bean; add bean. Bring to simmer.
Remove from heat, cover, and let steep 30 minutes.
Whisk yolks and sugar in medium bowl until thick. Gradually whisk half and half with vanilla bean into yolk mixture. Return mixture to same saucepan. Stir custard over low heat until thickened enough to leave path on back of spoon when finger is drawn across, about 6 minutes (do not boil).
Pour into bowl. Chill uncovered until cold, at least 2 hours. DO AHEAD: Can be made 1 day ahead. Cover; chill. Discard vanilla bean before using.
