In a measuring cup, measure out the eggnog and heavy whipping cream, and gently whisk them together until fully combined.

In a medium saucepan, whisk together granulated sugar, cornstarch, salt, and ground nutmeg until the mixture is smooth and well blended.

Add the egg yolks to the dry ingredients in the saucepan and whisk vigorously until completely smooth.

Gradually pour the eggnog and cream mixture into the saucepan while constantly whisking to combine.

Place the saucepan over medium heat, and cook the mixture while stirring constantly for 8-10 minutes until it thickens.

Remove the saucepan from the heat and stir in the rum extract and unsalted butter until fully melted.

Strain the pudding into a bowl using a fine-mesh sieve, discarding any lumps. Cover with plastic wrap touching the surface.

Chill the eggnog pudding in the refrigerator for at least 4 hours, preferably overnight.

Scoop the chilled eggnog pudding into bowls and top with whipped cream, grated nutmeg, and sugared cranberries.