In a saucepan over medium heat, combine half-and-half, 1/4 cup sugar and vanilla bean.
In a bowl, whisk together egg yolks and remaining 1/4 cup sugar until smooth.
When cream mixture comes just to a boil, remove from heat and remove vanilla bean. Whisk a small amount of hot cream into the egg yolk mixture, then pour egg yolk mixture into remaining hot cream and whisk until smooth. Return to medium heat and cook, stirring, until mixture coats the back of a metal spoon. Remove from heat and stir in butter. Serve warm or cold.