In a bowl, whisk together the flour, cocoa powder, ginger, baking soda, cinnamon, nutmeg and salt.
In a large bowl, cream the butter, brown sugar and molasses with an electric mixer. Add the egg white and mix well. With the mixer at low speed, or using a wooden spoon, stir in the dry ingredients until the dough is smooth. Shape into 2 discs. Cover with plastic wrap and refrigerate for 1 hour.
With the rack in the middle position, preheat the oven to 375°F (190°C). Line two baking sheets with parchment paper or silicone mats.
On a lightly floured surface, roll out one piece of dough at a time to a thickness of 1/8 inch (3 mm). Cut the cookies with a 4-inch (10 cm) holiday-themed cookie cutter. Place on the prepared sheets, spacing them evenly. Use the scraps.
Bake one sheet at a time for 8 minutes or until the edges of the cookies are slightly firm. Let cool completely.
Decorate the cookies with vanilla royal icing, if desired. The cookies will keep for 3 weeks in an airtight container at room temperature.