Special equipment: assorted snowflake cookie cutters (3-inch and 2-inch cutters)
In a medium bowl, whisk together the flour, baking powder, salt, 1/2 teaspoon of the cinnamon and the nutmeg. In a separate large bowl using an electric mixer, beat together the butter, 1 cup of the granulated sugar and the brown sugar, mixing until pale yellow and fluffy, 3 minutes. Add in the vanilla and eggs and mix well. Slowly incorporate the dry ingredients into the wet ingredients and mix well.
Transfer the dough to a floured work surface, divide into two disks, wrap in plastic and chill in the refrigerator for about an hour.
Preheat the oven to 350 degrees F. Line two baking sheets with parchment paper.
Working with one disk at a time, roll out the dough to 1/4-inch thickness. Cut out snowflake shapes with the cookie cutters and place the cookies about 2 inches apart on the prepared baking sheets (place snowflakes of the same size on each baking sheet). Re-roll the scraps to get as many cookies as possible, returning the dough to the refrigerator to chill if necessary.
In a small bowl, combine the remaining 1/2 cup granulated sugar and 1 1/2 teaspoons cinnamon. Sprinkle the cinnamon-sugar mixture over the snowflakes before baking.
Bake just until the edges start to brown, 10 to 12 minutes. (Bake one sheet at a time for even cooking and browning.) Transfer the cookies to a wire rack and let cool.
Decorate with royal icing if desired.