(adapted from Martha Stewart Cookies)
3 large egg whites
3/4 cup sugar
4-6 drops eggnog flavor candy oil, or to taste
Preheat oven to 175 degrees. Line 2 baking sheets with parchment paper; secure corners with masking tape. Fit a pastry bag with a small open-star tip (such as Ateco #22). Set aside. (A plastic bag with the corner cut off will work as well, but the cookies will not be quite as pretty.)
Put the egg whites and sugar in the heatproof bowl of an electric mixer. Set the bowl over a pan of simmering water, and stir gently until sugar has dissolved and mixture is warm to the touch, 2 to 3 minutes.
Transfer the bowl to an electric mixer fitted with the whisk attachment. Mix on medium-high speed until stiff peaks form. Mix in the flavoring.
Fill the pastry bag with 1 to 2 cups meringue. Pipe small (3/4-inch-high) star shapes onto prepared baking sheets. Refill bag as necessary.
Bake cookies until crisp but not brown, about 1 hour 40 minutes.* (They should no longer be sticky to the touch) Let cool completely on sheets on wire racks. Store cookies in an airtight container for up to two days.
* Note: There are many things that affect how quickly the cookies will bake. On a humid day they may need more time. Additionally, many ovens do not hold temperature accurately at such a low temperature so the cooking time can vary up to an hour. Start checking after about an hour and a half but be prepared to bake them quite a bit longer if necessary.