To make the cookies, cream the butter, sugar, vanilla bean seeds, vanilla extract and almond extract in a large bowl or bowl of a stand mixer until light and fluffy, about a full 3-5 minutes.: The aroma at this stage should be sweet and fragrant, with the unsalted butter and granulated sugar turning pale and airy, which signals trapped air for lift. You will notice tiny bubbles in the mix and a lighter color, this is the visual cue you want. The sound is a gentle, steady whir from the mixer rather than a harsh grinding, meaning the ingredients are combining smoothly. This creaming step matters because it sets the structure and texture, helping cookies be tender rather than dense. A common mistake here is undercreaming, which yields heavy cookies, or overcreaming, which can make the dough too soft; stop once the mix looks pale and holds texture. If the mixture starts to look greasy, pop the bowl in the fridge for 10 minutes to firm the butter.
Add the egg and eggnog and mix until evenly combined. Add half the flour, baking soda and salt, beating until combined. Then add the remaining flour and beat until the dough forms a ball.: You should smell a richer, custardy note from the egg and eggnog at this point, and the batter will change from fluffy to more cohesive, slightly glossy and smooth to the touch. The tactile cue is a dough that pulls together but is not sticky. The reason for adding flour in two parts is to avoid overmixing the gluten, which keeps cookies tender. Watch for a dough that just comes together, a common error is overbeating after the flour which toughens the result. If the dough seems too sticky, rest it briefly in the fridge to firm up before rolling.
Generously flour your work surface. Divide the dough in half and flatten each half into a disk.: The cool, slightly firm disks make them easier to roll and cut; you should feel a pliable, cool dough that does not stick to your hands. Flour the board until it looks dusted but not buried, and press the dough into even disks so they chill uniformly. This step is about control, because a warm, soft disk will spread too much. A typical problem is skipping the flour and having the dough cling to the rolling pin; using a light dusting prevents that without drying the dough out.
Roll out the dough to 1/4 inch thickness. Make sure you are using enough flour or your dough will stick. You can also roll the dough out between two pieces of wax paper. Cut out the cookies into your desired shapes. Carefully transfer the cookies to a parchment lined baking sheet. Cover the baking sheet and place the baking sheet in the freezer, freeze until very firm, about 25 minutes. Roll out the leftover scraps, and repeat with the remaining disk of dough.: As you roll, notice the dough surface becoming smooth and slightly cool to the touch; this indicates the right temperature. The even 1/4 inch thickness is the key visual cue, as any thinner will brown too quickly and any thicker will change the bake time. Using wax paper helps prevent sticking and keeps edges clean. Transferring the shapes carefully to the baking sheet keeps them intact; I use a thin spatula for this. The freezing step firms the fats so the cookies hold their shape and yields a clean edge after baking. A common mistake is underfreezing, which allows shapes to spread and lose definition.
Preheat oven to 350 degrees.: You will feel the kitchen warm and smell a faint dry heat as the oven reaches temperature, and a steady, accurate preheat is essential so the cookies begin baking immediately with consistent oven spring. Preheating also ensures the first cookies do not overbake while the oven warms. An error to avoid is putting the pan in before the oven is fully hot, which alters timing and texture. Use an oven thermometer if your oven runs cool or hot to get predictable results.
Bake the cookies on the middle rack of the oven for 12-15 minutes or until just lightly golden brown. Do not over bake. Cool on the baking sheet five minutes and then transfer to a wire cooling rack to cool completely.: When correctly baked you will see faint golden edges and a set center, and the smell will be warm, buttery, and spiced. The sound when you tap the edge is a quiet, firm click, not a hollow ring. Letting them cool on the sheet for five minutes lets them finish gently while setting; moving them too soon risks breakage. Overbaking is the most common issue, leading to dry cookies, so pull them when they still look slightly pale in the center.
To make the icing, combine the sugar and meringue powder in the bowl of an electric mixer fitted with the paddle attachment. Mixing on low speed, add 6 tablespoons water. Mix until icing holds a ribbon-like trail on the surface of the mixture for 5 seconds when you raise the paddle. Add the vanilla bean seeds and nutmeg, mix until just combined.: The texture you want is glossy and smooth with a slow, ribbon like fall from the paddle, which indicates the right viscosity for flooding and piping. You will notice a sweet, spiced perfume as the vanilla bean and nutmeg integrate. This stage matters because the right consistency ensures the icing sets without cracking. A frequent mistake is adding too much water at once, making the icing runny; add it slowly and test the ribbon. If the icing stiffens, a few drops of water will revive it.
Frost the cooled cookies and decorate as desired. I like to keep things simple and use holiday sprinkles to decorate most of my cookies. You can also use food coloring and color the frosting red, green or whatever colors you like. To pipe the icing onto the cookies, add the icing to a gallon size ziploc bag (or a piping bag), then snip off a small portion of the corner off.: When you frost, the smooth, cool feel of the icing meets the cookie and creates a slight sheen; the frosting should settle and firm within an hour depending on humidity. Decorating is where you can be playful, adding sprinkles or a thin piped border for definition. The why here is presentation and texture contrast, as the firm icing pairs with the tender cookie. A common issue is decorating while the cookies are warm, which causes the icing to melt and slide off; always frost completely cooled cookies.