1. Combine Ingredients: In a medium saucepan, whisk together the eggnog, heavy cream, sugar, cornstarch, salt, and nutmeg until smooth.

2. Heat Mixture: Place the saucepan over medium heat and cook, stirring constantly, until the mixture thickens and begins to bubble.

3. Temper Egg Yolks: In a small bowl, whisk the egg yolks. Gradually add a few tablespoon of the hot eggnog mixture to the yolks, whisking constantly, then pour the yolk mixture back into the saucepan.

4. Cook Further: Continue cooking and stirring for 2–3 minutes until the pudding is thickened.

5. Finish: Remove the saucepan from the heat and stir in the rum extract and butter until fully incorporated.

6. Chill: Pour the pudding into serving dishes. Cover with plastic wrap directly on the surface to prevent a skin from forming. Chill in the refrigerator for at least 2 hours.

7. Serve: Top the chilled eggnog pudding with whipped cream, grated nutmeg, and sugared cranberries, if desired.