1. Whisk together 3-1/2 cups flour, 1 teaspoon baking soda, 1/4 teaspoon salt, and 1 teaspoon of each spice in a medium bowl.
2. Beat together 1 stick butter and 1/2 cup brown sugar in a large bowl on medium speed until light and fluffy, about 3 minutes. Add 1 egg, 1/4 cup plus 2 tablespoons molasses, and 1/4 cup syrup; beat mixture until combined well. Reduce speed to low and gradually add flour mixture, beating until just combined.
3. Transfer to a lightly floured surface and knead until dough holds together. Divide and flatten into 2 (7-inch) disks, wrap each well in plastic wrap and chill until firm, about 1 hour. Meanwhile, repeat to make a second batch of dough.
4. Preheat oven to 350 degree F and arrange racks in upper and lower thirds.
5. Working with 1 disk at a time (keeping remaining disks chilled), unwrap and let dough soften slightly, about 5 minutes. Roll out dough on a lightly floured surface with a floured rolling pin until 1/4 inch thick to make reindeer, sleigh, and tree cutouts.For reindeer and sleigh::
6. Dough must be precisely 1/4 inch thick. (If too thin, the reindeer won't stand up; if too thick, the parts won't fit together.) Following the manufacturer's directions, cut out 8 reindeer and 1 sleigh. Press together dough scraps and flatten into a disk; wrap well in plastic wrap and chill until firm, about 20 minutes, for additional cutouts.
7. Transfer cutouts to 4 ungreased cookie sheets, arranging smaller and larger pieces in separate trays, placing 1-1/2 inches apart.
8. Bake, 2 sheets at a time, switching sheets halfway through, until golden, 10 to 14 minutes, depending on size of cookies. Transfer cookies on sheets to racks and cool until firm, about 2 minutes. Using a metal spatula, transfer cookies to racks and cool completely.For trees::
9. Working with 1 disk at a time, roll out dough (as above). Each assembled tree requires 2 identical cookies. Keeping that in mind, cut out 2 cookies (using the same cutter) for each tree, making a total of 32 cookies for 16 trees. Press together dough scraps and chill (as above), for additional cutouts.
10. Cut trees in half and carefully transfer to 2 ungreased cookie sheets, placing 1-1/2 inches apart.
11. Bake, switching cookie sheets halfway through, until pale golden, about 10 minutes. Transfer cookies on sheets to racks and cool until firm, about 2 minutes. Using a metal spatula, transfer cookies to racks and cool completely.
12. To assemble reindeer and sleigh: Attach the #11 pastry tip to icing tube and assemble cookies according to manufacturer's directions. Using icing, attach M&M's to reindeer noses.
13. To assemble trees: Attach the #9 pastry tip to icing tube. Using 4 halves of 2 trees (cut from same cutter), squeeze a line of icing along trunk edge of matching half and press together. Squeeze another line of icing on edge of third half and attach to center; repeat with fourth half. Repeat to make 15 more trees. Stand trees up on a cookie sheet and let dry completely, at least 2 hours or overnight.
14. To assemble forest: Sprinkle a serving tray with confectioners' sugar. Dip tree edges in sugar. Arrange reindeer, sleigh, and trees on tray. (Can be stored at room temperature in an airtight container up to 3 weeks.) Makes 8 reindeer, 1 sleigh, and about 16 trees.