01 - In a medium bowl, whisk together flour, cocoa powder, cinnamon, baking powder, and salt until evenly blended.
02 - In a large bowl, beat butter and granulated sugar 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 the wet mixture, mixing on low speed just until a cohesive dough forms. Avoid overmixing to prevent tough cookies.
04 - Divide dough in half and shape each portion into a flat disk. 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 - On a lightly floured surface, roll out dough to 1/4-inch thickness. Cut out skeleton or gingerbread man shapes using cookie cutters. Transfer to prepared baking sheets, spacing 1 inch apart.
07 - Bake for 10-12 minutes until edges are set. Let cool on baking sheets for 2 minutes before transferring to a wire rack to cool completely.
08 - In a clean bowl, beat egg white with powdered sugar until smooth. Add water 1 tablespoon at a time, mixing until icing reaches pipeable consistency.
09 - Transfer icing to a piping bag fitted with a fine round tip. Pipe skeleton designs onto cooled cookies. Allow icing to dry completely before storing or serving.