1. In a medium bowl, whisk together flour, cornstarch, cinnamon, and salt.
2. In mixer bowl, cream butter, eggnog and icing sugar together until smooth and fluffy. About 2 minutes.
3. Turn mixer on low and slowly add flour mixture. Continue to mix on low until dough comes together. Be careful not to overmix.
4. Roll dough between two pieces of parchment paper to about 1/4" - 1/2" thickness depending on your preference. Refrigerate rolled out dough for at least 1 hour.

5. Once chilled, preheat oven to 375 degrees F. Line 2-3 large baking sheets with parchment paper or a silicone baking mat. Remove dough from the refrigerator and using a cookie cutter, cut in shapes. Transfer the cut cookie dough to the prepared baking sheet about 1/2 inch apart.

6. Bake for 10-13 minutes until cookies are slightly golden on bottom edges. Cool on a wire rack.
7. Re-roll the remaining dough and continue cutting until all the dough is used up.

Make the Glaze:

1. Whisk icing sugar and ground cinnamon into eggnog until it becomes smooth and creamy. Once cookies have cooled, place on parchment paper and use a spoon to drizzle or spread glaze over each one. Top with sprinkles, cinnamon sugar or sanding sugar as desired. Allow the glaze to harden (approximately an hour) before serving.