Stir together the flour, salt, and baking powder and set aside.
In the bowl of an electric mixer fitted with a paddle attachment, cream the butter, shortening, and granulated sugar until light. Scrape the bowl, add the egg, and beat just until combined. Add the flour mixture all at once and incorporate, making sure to only beat until combined. Scrape the dough onto plastic wrap and refrigerate until firm, at least 2 hours.
When ready, preheat the oven to 350 degrees, remove the dough from the fridge, and break off walnut-sized pieces. Roll them into irregular rounds with your hands. You’re making rocks. The great part is that they can’t be too perfect!
Roll out another chunk of dough on a floured surface about ¼-inch thick and cut long strips about ¼-inch wide by 4-5 inches long. Bend and twist them to look like sticks. You can cut little notches in them as well.
Or, take a golf ball-sized piece of dough and roll the dough between your palms and the counter to form a long snake. Cut off 4- to 5-inch portions and bend into sticks. Bake the cookies for about 10-12 minutes until lightly golden.
While they are baking, stir together the powdered sugar and cocoa powder. Also, leave some powdered sugar in a bowl by itself. Have a sifter nearby; you will need it when the cookies come out of the oven.
When you remove them from the oven, immediately sift the sugar-cocoa combination over some of the sticks and rocks. Sift the plain powdered sugar over others. You can also leave some plain. Stick the cookies in a basket so they look all spiky. Remember to store them in an airtight container.