In a large heavy saucepan, scald the milk and sugar over medium-low heat.
Stir in orzo and cook, stirring frequently and adjusting heat to prevent milk from boiling over, until mixture is thickened and orzo is tender to bite, about 20 to 25 minutes.
Meanwhile, beat egg in a medium bowl.
Stir raisons, lemon zest and vanilla into th epudding until blended.
Gradually add the hot pudding to the beaten egg, stirring constantly so that the egg doesn't curdle.