01 - Whisk together flour, cocoa powder, cinnamon, baking powder, and salt in a medium bowl until thoroughly combined.
02 - Beat butter and sugar in a large bowl until light and fluffy, approximately 2 minutes. Incorporate egg and vanilla extract, mixing until fully blended.
03 - Gradually add dry ingredients to wet mixture, mixing just until dough comes together. 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 until firm.
05 - Preheat oven to 350°F. Line baking sheets with parchment paper and set aside.
06 - Roll chilled dough to 1/4-inch thickness on lightly floured surface. Cut skeleton shapes using cookie cutter and transfer to prepared baking sheets.
07 - Bake for 10-12 minutes until edges are set. Cool completely on wire rack before decorating.
08 - Beat egg white with powdered sugar and water until smooth and pipeable consistency is achieved. Adjust with additional water if necessary.
09 - Transfer icing to piping bag fitted with fine tip. Pipe skeleton designs onto cooled cookies and allow icing to dry completely before serving.