Sift the flour, cocoa powder, salt, cinnamon, baking powder, chile powder, and black pepper into a large bowl. 

In the bowl of a standing mixer fitted with the paddle attachment, cream the butter, shortening, and sugar until light and fluffy. Scrape down the sides of the bowl and, working with the mixer on lmedium-ow speed, add the egg, vanilla, and melted chocolate and mix until thoroughly combined. 

Scrape down the sides of the bowl and, with the mixer on low speed, add the flour in two additions, mixing only until each addition is incorporated. Scrape down the sides of the bowl and then divide the dough into two equal portions, placing each half onto a sheet of plastic wrap. Gather the edges of the wrap over the dough and flatten to form a smooth, round disk. Refrigerate for at least 2 hours, or until firm.

Working on a clean, well-floured work surface, roll each disk of dough into a thickness of 1/4-inch using a floured rolling pin and adding flour to the top of the dough as necessary to keep it from sticking. You may need to reposition the dough a couple of times and reflour the work surface if the dough begins sticking. Using a skull-shaped cookie cutter, cut as many cookies out of the dough as possible and transfer the cookies to parchment-lined baking sheets. Gather and reroll any scraps if desired. You should be able to get about 18 3- or 4-inch cookies. Transfer the baking sheets to the freezer for at least 15 minutes. Preheat the oven to 325 degrees F. 

Bake the cookies in the middle of the oven, rotating the baking sheets back to front mid-way during cooking, until the cookes are set around the edges and lightly dry on top, usually 12 to 14 minutes. Allow the cookies to cool on the baking sheets for 10 minutes, then carefully transfer them to cooling racks until completely cool before icing. 

In the bowl of a standing electric mixer fitted iwth a paddle attachment, combine 6 1/2 cups of the powdered sugar along with the cream of tartar, egg whites, and lemon juice. Mix on low speed just until the sugar is smooth and any lumps are gone, then increase the speed slightly and mix until the icing is smooth and glossy. It should be thick enough to hold a line on a cookie but also thin enough to spread and pour. You will know when you begin working with it if you need to thin it by adding a bit more egg white or lemon juice (a teaspoon at a time) or if it is too thin, in which case you can add a spoon more of powdered sugar at a time. Transfer a small amount of the icing to a small piping bag fitted with a tiny plain round tip. Carefully line the edge of each cookie with a line of the white icing. By the time you have finished outlining all of the cookies, you can then go back and fill the inside of each outlined cookie with the white icing, adding enough icing to spread and completely cover the top of the cookie. You might find that you need to use a tiny paintbrush to help smooth the icing out to cover all of the outlined area. The back of a tiny spoon (or the spoon handle) might also help if you don't have a paintbrush handy. Once all of the cookies are painted white on top, set them on a rack and allow them to dry, undisturbed, for at least 8 hours and up to overnight. The remaining white icing should be refrigerated in airtight containers until you are ready to decorate the cookies.

The next day, remove the icing from the refrigerator about an hour before you plan to decorate the cookies. Divide the icing into 6 or 7 small bowls and tint each bowl a different color by using the gel food dyes. Keep the bowls covered until you are ready to begin decorating. 

Draw eyes, mouths, and noses on each cookie and decorate as desired using small candies (if desired) and the colors you like best. The tinier the pastry tip that you use, the finer the lines you will be able to make. If the icing has thickened too much to flow easily onto the cookies, add a bit more lemon juice or egg white to thin it slightly. Decorate the cookies as detailed or simple as you like. Traditional Day of the Dead cookies and sugar work is very detailed, but simple designs can be just as eye-catching. Make them your own!

Set the cookies aside to dry completely before putting them on a plate to serve.