Combine 2 cups of eggnog and 1 cup of heavy whipping cream in a large glass measuring cup. Stir gently and set aside.

In a medium saucepan, whisk together 3/4 cup of granulated sugar, 1/4 cup of cornstarch, 1/4 teaspoon of salt, and 1 teaspoon of ground nutmeg until blended.

Add 4 large egg yolks to the dry mixture, whisking vigorously until smooth with no lumps.

Gradually pour the eggnog and cream mixture into the saucepan while whisking continuously to prevent curdling.

Place over medium heat and stir constantly for about 8–10 minutes until thickened enough to coat the back of a spoon.

Remove from heat, add 2 tablespoons of unsalted butter and 1 teaspoon of rum extract, stirring until smooth.

Strain the mixture through a fine mesh sieve into a heatproof bowl to ensure a silky texture.

Cover with plastic wrap pressed onto the surface and refrigerate for at least 4 hours or overnight.

Prepare toppings, such as whipping cream until fluffy peaks form, and chill any garnishes ahead of time.

Serve the chilled pudding in decorative glasses, top with whipped cream and desired toppings.