In a medium saucepan, combine the eggnog, whole milk, and granulated sugar. Place the saucepan over medium heat and stir continuously until the mixture is warm but not boiling, about 5 minutes.
In a separate small bowl, mix the cornstarch with a few tablespoons of the warm eggnog mixture to create a smooth slurry. This will help incorporate the cornstarch without clumping.
Slowly pour the cornstarch slurry back into the saucepan with the warm eggnog mixture, whisking vigorously to ensure a lump-free consistency.
Keep stirring the mixture over medium heat until it thickens to a pudding-like texture, which should take approximately 5-7 minutes. You’ll know it's ready when it coats the back of a spoon.
Once the pudding has thickened, remove the saucepan from the heat. Stir in the vanilla extract, freshly grated nutmeg, and ground cinnamon until everything is well blended.
Allow the pudding to cool for about 10 minutes, stirring occasionally to avoid a skin forming on the surface.
Carefully spoon the pudding mixture into small shot glasses or cups, filling them about three-quarters full to allow room for the whipped cream.
Place the pudding shots in the refrigerator and chill for at least 2 hours, or until they are fully set and firm to the touch.
When ready to serve, generously top each pudding shot with a dollop of whipped cream and finish with a light sprinkle of extra nutmeg or cinnamon for a festive touch.
Notes
Serve the pudding shots on a decorative platter with a festive garnish of cinnamon sticks or sprigs of mint for a cheerful holiday display.