01 -
In a large bowl, whisk together the flour, ground ginger, cinnamon, ground nutmeg, ground cloves, baking soda, and salt. Set aside.
02 -
In a separate large bowl, beat together the unsalted butter and brown sugar using an electric mixer on medium speed until smooth. Add the egg, egg yolk, vanilla extract, and molasses, mixing until fully combined.
03 -
Gradually mix the dry ingredients into the wet ingredients on low speed until fully combined. Scrape down the sides of the bowl as necessary. Cover the dough with cling wrap and refrigerate for 30 minutes or up to 24 hours.
04 -
When ready to bake, remove the dough from the fridge. Preheat the oven to 175°C (350°F) and line two cookie sheets with parchment paper or silicone baking mats. If the dough has been chilled for over 2 hours, allow it to soften at room temperature for about 20 minutes.
05 -
Form the dough into balls about 1.5 tablespoons in size. Roll each dough ball in granulated or turbinado sugar and place on the cookie sheet, spaced 5 centimeters (2 inches) apart. Bake for 8-10 minutes until the tops are just set. Cool on the baking tray for 5-10 minutes, then transfer to a wire rack to cool completely.
06 -
In a medium bowl, beat the butter on medium speed until soft and smooth. Beat in the icing sugar 1/2 cup at a time until 2 cups have been added. Add the eggnog 1 tablespoon at a time, plus the optional rum extract, until the desired consistency is achieved. Adjust sweetness by adding more powdered sugar or eggnog as necessary. The frosting should be smooth and spreadable.
07 -
Frost the bottom of one cookie with about 1 tablespoon of eggnog frosting, then place a second cookie on top. Continue assembling until all cookies are completed, resulting in 16-18 sandwich cookies.