In a large heavy saucepan, scald the milk and sugar over medium-low heat

Stir in the orzo and cook, stirring frequently and adjusting heat to prevent milk from boiling over and scorching, until mixture is thickened and orzo is al dente, about 20 to 25 minutes

Meanwhile, beat the egg in a medium bowl

Stir the raisins, lemon zest, and vanilla into the pudding until blended

Gradually add the hot pudding to the beaten egg, stirring constantly with a spoon so that egg doesn't curdle

Sprinkle with nutmeg

Cool slightly at room temperature

Serve warm

Pudding will thicken and set upon cooling.