01 - Whisk together flour, cocoa powder, cinnamon, baking powder, and salt in a medium bowl until thoroughly combined.
02 - Beat softened butter and granulated sugar in a large bowl with an electric mixer until light and fluffy, approximately 2 minutes. Add egg and vanilla extract; mix until fully incorporated.
03 - Gradually add dry ingredients to wet mixture, mixing on low speed just until dough comes together. Avoid overmixing.
04 - Divide dough in half and shape into disks. Wrap tightly in plastic wrap and refrigerate for at least 30 minutes until firm.
05 - Preheat oven to 350°F. Line baking sheets with parchment paper and set aside.
06 - Roll chilled dough on lightly floured surface to 1/4-inch thickness. Cut out skeleton or gingerbread man shapes using cookie cutters.
07 - Arrange cutouts on prepared baking sheets. Bake for 10-12 minutes until edges are set. Allow to cool completely on wire racks.
08 - Beat egg white with sifted powdered sugar and 2 tablespoons water until smooth. Adjust consistency with additional water as needed to achieve pipeable texture.
09 - Transfer icing to piping bag fitted with fine round tip. Pipe skeleton designs onto cooled cookies. Allow icing to dry completely before serving or storing.