In medium bowl, whisk together flour, cocoa powder, cinnamon and salt until well combined.

In large bowl, beat butter and powdered sugar on medium speed 1 minute until pale and fluffy. Beat in egg and vanilla. Stir in flour mixture until just combined.

Shape dough into disc, then wrap in plastic wrap. Refrigerate at least 1 hour.

Heat oven to 350 degrees F. On lightly floured surface, roll out dough to 1/8-inch thickness. Use oval, egg or skull-shaped cookie cutter to cut dough into shapes. Space cookies 2 inches apart on parchment paper-lined baking sheets. Refrigerate until firm, about 15 minutes.

Bake cookies 8 to 10 minutes until crisp and set. Transfer to cooling rack to cool completely.

To make icing: In small bowl, stir powdered sugar and milk until well combined. Transfer to quart-size resealable plastic bag. Snip off one end.

Outline cookie edges with icing, leaving small border. Fill in center with more icing, using toothpick to spread out icing.

Decorate cookies with assorted candies, sprinkles, etc.