Chocolate Shortbread Cookies

Chocolate Shortbread Cookie Dough
2 Preheat oven to 375℉ (190℃) and line two cookie sheets with silicone baking mats or parchment paper.
3 In a large bowl beat together softened butter and confectioner's sugar with a hand mixer. Start on low and increase to medium as the sugar starts to blend into the butter, about 2-3 minutes. Scrape bottom and sides of bowl with rubber spatula as needed.
4 Add the egg, bourbon, and vanilla mixing until distributed.
5 Using a medium bowl whisk together the sifted flour and cocoa with the baking powder, salt, cinnamon, nutmeg, cardamom, and espresso powder.
6 Mixing on low speed, spoon the flour mixture into the butter mixture until a cookie dough is formed. If it seems clumpy, just pat together with you hands to form a large ball of dough.
7 The dough should not be dry and crumbly, nor wet. But, a nice soft smooth texture that does not stick to your hands and packs well. 
8 Divide the dough in half. Then wrap one half in plastic wrap and set aside.
9 Dust your work surface and rolling pin with confectioner's sugar. I find that flour dries out the dough, so I prefer to roll my cookies out on confectioner's sugar instead.
10 Shape cookie dough into a disc with your hands. Roll out to 1/4 inch thickness.
11 Cut with the 5 gradual sized snowflake cookie cutters. Making sure to cut out 3 of each shape for your cookie tree.
12 Place cookies on baking pans spacing 1.5 inches apart. 
13 Bake on middle oven rack for 7-9 minutes. Be careful not to over bake your cookies. Remove when the edges are a bit darker than the rest. (Yes, chocolate cookies are harder to tell, but they should be thick, well shaped and have a slight crinkle on the top). They will be slightly soft when warm, but firm as they cool. (8 minutes was the sweet spot for me)
14 Place pans on wire cooling rack for 1-2 minutes. Then carefully transfer cookies directly onto rack using a rubber spatula to completely cool.
15 Repeat with remaining half of cookie dough.
16 Pipe cooled cookies with royal icing in desired designs. Let icing dry and firm.
Assemble Cookie Tree
19 With the first set of cookies start with the largest snowflake first. Stack cookies from biggest to smallest, twisting them ever so slightly to keep the points from lining up. 
20 You can use 3 of each size to create your tree. Or 4 if you aren't planning on making 2 duplicate trees.
21 Pipe royal icing onto the center of each cookie as you stack them to act as a glue to hold them together. You can also stack a few cookies, let them set and then move on to the next.
22 For the vertical "star" on the very top, use royal icing on the center of the last cookie then stand the little "star" upright to act as the tree topper.
23 Repeat with remaining cookies for a second cookie tree.