Preheat your oven to 350°F (175°C). This ensures your cookies will bake evenly and come out perfectly golden brown.

Cream together the softened butter, granulated sugar, and brown sugar in a large bowl until light and fluffy. This step is crucial for achieving that melt-in-your-mouth texture!

Mix in the egg yolk, vanilla extract, ground cinnamon, ground nutmeg, and eggnog until everything is well combined.

Gradually add the all-purpose flour and baking soda to the bowl, mixing until just combined.

Scoop tablespoon-sized dough balls and roll them in a mixture of cinnamon and sugar for that signature snickerdoodle touch.

Place the dough balls on a lined baking sheet, spacing them about 2 inches apart. Press your thumb gently in the center of each ball to create an indentation.

Bake for 10-12 minutes, or until the edges are set and the centers remain soft.

Prepare the frosting by whisking together the powdered sugar and milk until smooth.

Once cooled, pipe or spread the creamy frosting onto the center of each cookie.

Dust with additional cinnamon for a lovely presentation!