These rich, flavorful cookies are a classic holiday cookie for a reason: they're delicious and can be decorated countless ways! Remember to give yourself plenty of time to chill the dough before rolling and cutting. Adapted from a recipe by Cook's Illustrated.
In a food processor or mixer with the paddle attachment combine flour, brown sugar, spices, baking soda and salt. Add the butter and pulse or mix until the mixture resembles sand.
With the processor or mixer running, add the molasses and milk and mix until the dough is evenly moistened. Remove the dough, wrap tightly in plastic and chill for at least 2 hours or overnight. Meanwhile, preheat oven to 325°F and line two baking sheets with parchment paper.
After chilling, remove the dough from the refrigerator and divide into two sections. Keep one piece chilled while working with the other. Roll the dough between two pieces of parchment paper to about 1/8-inch thickness, carefully removing and replacing the parchment paper as needed to reduce sticking. Cut the dough into desired shapes but leave the cookies on the parchment paper. Return to the refrigerator to chill, and repeat with the remaining dough.
After both pieces of dough have been rolled, cut and chilled, carefully remove the cutout cookies from the parchment sheets using a flat spatula and transfer to the prepared baking sheets. The scraps of dough can be rerolled and chilled for more cookies.
Bake the cookies in the preheated oven until the centers are firm, about 15-20 minutes, rotating the sheets about halfway through the baking time. Let cool completely before decorating.
While the cookies are cooling, prepare the royal icing. In the bowl of a mixer, beat the egg white and vanilla extract until frothy. Gradually add the powdered sugar and mix on low until shiny (add any food coloring as desired at this time). Increase the mixer to high and beat until stiff and glossy, 5-7 minutes. Decorate cooled cookies as desired.
