1.Combine milk, cream and vanilla bean in medium saucepan; heat until just below boiling point. Stand 15 minutes; remove vanilla bean.
2.Beat egg yolks and sugar in small bowl with electric mixer until thick and creamy. Gradually whisk hot milk mixture into egg mixture.
3.Return milk mixture to pan, stir over low heat, without boiling, until custard thickens and coats the back of a metal spoon. Stir in liqueur.