1. Prepare the crust by combining the graham cracker crumbs or crushed spiced cookies with the granulated sugar in a medium bowl.

2. Pour in the melted butter and stir until the crumbs are evenly moistened and the mixture resembles damp sand.

3. Divide the crumb mixture evenly among 6 to 8 small glasses or dessert cups and press it firmly into the bottom of each to create a crust. Refrigerate the cups while you prepare the mousse.

4. In a large mixing bowl, beat the softened cream cheese with the powdered sugar using a hand mixer or stand mixer until very smooth and creamy with no lumps.

5. With the mixer on low speed, slowly stream in the chilled eggnog, scraping down the sides of the bowl as needed, until the mixture is silky and well combined.

6. Add the vanilla extract and ground nutmeg, then mix again until the flavors are evenly distributed. Taste and adjust the nutmeg if you prefer a stronger spice flavor.

7. In a separate chilled bowl, whip the heavy whipping cream to medium stiff peaks, where the cream holds its shape but the tips curl slightly.

8. Gently fold the whipped cream into the eggnog cream cheese mixture in two or three additions, using a spatula to lift and turn the mixture without deflating it.

9. Spoon or pipe the eggnog mousse over the chilled crumb crusts, filling each glass almost to the top and smoothing or swirling the surface as desired.

10. Cover the glasses and refrigerate the Eggnog Mousse Cups for at least 2 hours, or until the mousse is set and thoroughly chilled.

11. Just before serving, whip the remaining heavy cream with the powdered sugar until soft peaks form, then pipe or spoon it over each mousse cup.

12. Finish with a light dusting of ground cinnamon or additional nutmeg and serve the cups well chilled.