Creating Eggnog Snickerdoodle Thumbprint Cookies is a fun and rewarding experience. Follow these steps for a perfect batch:

1. Preheat Oven: Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper.
2. Mix Dry Ingredients: In a medium bowl, sift together the flour, baking soda, salt, cinnamon, and nutmeg. Set aside.
3. Cream Butter and Sugar: In a large bowl, beat the softened butter and granulated sugar with an electric mixer until light and fluffy.
4. Add Eggs and Vanilla: Add the eggs, one at a time, and beat well after each addition. Mix in the vanilla extract until well combined.
5. Combine Mixtures: Gradually add the flour mixture to the wet ingredients, alternating with the eggnog. Mix until just combined.
6. Shape Cookies: Scoop tablespoon-sized amounts of dough and roll them into balls. Place them on the prepared baking sheets.
7. Create Thumbprints: Use your thumb or the back of a teaspoon to create an indentation in the center of each cookie.
8. Bake: Bake in the preheated oven for 10-12 minutes, until the edges are lightly golden. Remove from the oven and allow to cool on baking sheets for 10-15 minutes.
9. Prepare Filling: While the cookies cool, whisk together powdered sugar and a tablespoon of cream or milk until smooth.
10. Fill Cookies: Once cooled, spoon a small amount of the filling into each thumbprint indentation.
11. Dust with Sugar: For an extra festive touch, dust the cookies with powdered sugar before serving.

These steps will ensure your Eggnog Snickerdoodle Thumbprint Cookies turn out perfectly every time!