01 - Whisk together flour, cocoa powder, cinnamon, baking powder, and salt in a medium bowl until thoroughly blended.
02 - Beat butter and granulated sugar in a large bowl until light and fluffy, approximately 2 minutes. Incorporate egg and vanilla extract, mixing until fully combined.
03 - Gradually add dry ingredients to wet mixture, mixing just until dough forms. Avoid overmixing to prevent tough cookies.
04 - Divide dough in half and flatten into disks. Wrap tightly in plastic wrap and refrigerate for minimum 30 minutes to firm.
05 - Preheat oven to 350°F. Line baking sheets with parchment paper and set aside.
06 - Roll dough to 1/4-inch thickness on lightly floured surface. Cut shapes using skeleton or gingerbread man cookie cutter.
07 - Arrange cutouts on prepared baking sheets. Bake for 10-12 minutes until edges are set. Transfer to wire rack and cool completely.
08 - Whisk egg white, powdered sugar, and water in bowl until smooth and pipeable. Adjust consistency with additional water if needed.
09 - Transfer icing to piping bag fitted with fine tip. Pipe skeleton designs onto cooled cookies. Allow icing to dry completely before serving.