Combine 1 cup of eggnog and 1 cup of heavy whipping cream in a large glass measuring cup. Stir gently to blend and set aside to reach room temperature.

In a medium saucepan, whisk together ¾ cup of granulated sugar, ¼ cup of cornstarch, a pinch of salt, and ½ teaspoon of ground nutmeg until no lumps remain.

Add 4 large egg yolks to the dry mixture, whisking vigorously until smooth.

Gradually pour the eggnog mixture into the saucepan while whisking continuously.

Place the saucepan over medium heat and stir constantly until the mixture bubbles and thickens, about 8-10 minutes.

Stir in 1 teaspoon of rum extract and 2 tablespoons of unsalted butter until melted and integrated.

Pour the pudding through a fine mesh sieve into a clean bowl to remove any lumps.

Cover the pudding with plastic wrap pressed directly against the surface and chill for at least 4 hours.

Serve by spooning the pudding into bowls or glasses, topping with whipped cream, grated nutmeg, and sugared cranberries.