Whisk egg yolks and sugar in a bowl until blended.
Split vanilla bean piece lengthwise; scrape seeds into cream using knife blade. Bring cream and vanilla bean seeds just to a boil in a medium-size heavy saucepan; reduce heat, and simmer 4 minutes. Stir one-fourth of hot milk mixture gradually into yolks; add yolk mixture to remaining milk mixture, stirring constantly. Cook over medium-low heat, stirring constantly, 6 minutes or until custard reaches 160° and coats the back of a spoon. Remove from heat, and set aside to cool. Store in refrigerator.