1. In bowl, mix flour, cocoa, cinnamon and salt. In large bowl, beat butter and sugar until fluffy, 2 minutes. Beat in egg and vanilla. On low, beat in flour mixture in thirds, until dough forms. Shape into disk. Halve dough; wrap each in plastic; chill at least 30 minutes or up to 2 hours.
2. Heat oven to 350 degrees F. Roll out dough to 1/4-inch thickness. Cut into 2-1/4-inch circles and 3-inch trees. Place on ungreased baking sheets.
3. Bake in 350 degrees F oven 11 to 13 minutes or until lightly browned around edges. Transfer cookies to wire rack; let cool.
4. In microwave-safe glass bowl, heat chocolate in 30-second increments, stirring until melted. Dip round cookies into melted chocolate to coat half of each cookie; let excess drip back into bowl. Dip edges of trees into chocolate. Place cookies on waxed paper; let set. Store airtight for up to 1 week.