Preheat the oven to 350. Line two baking sheets with parchment or spray with cooking spray. In a small bowl, whisk together the flour, corn starch, salt, cinnamon, and nutmeg. In a large bowl or the bowl of a stand mixer, beat together the butter and powdered sugar until light and fluffy. Add the rum extract, vanilla, and eggnog, and mix to combine. Add the dry ingredients and mix to form a thick dough.