In a medium-size bowl, thoroughly whisk cornstarch into 1/2 cup
of the milk. Let rest for 1 minute, then whisk again. Whisk in egg
In a medium-size saucepan, combine remaining 1 1/2 cups milk, sugar,
rum and vanilla extract and bring to a scald over medium heat. Whisking
constantly, slowly drizzle the hot liquid into the egg mixture.
Return the mixture to the saucepan and cook over medium heat, whisking
constantly and scraping the bottom of the pan, until tiny bubbles
boil up for 10 seconds.
Strain through a fine strainer into a bowl. Fold in the raisins.
Divide the pudding among 6 serving bowls.
Let cool to room temperature,
then cover and refrigerate until chilled.