1.Preheat oven to 350. Whisk together flour, cocoa powder, baking powder, and salt in a medium bowl; set aside. 2.Put butter and sugar into the bowl of an electric mixer fitted with the paddle attachment. Mix on medium-high speed until pale and fluffy. Mix in shortening. Add egg , rum and vanilla; mix until creamy. Reduce speed to low. Gradually add flour mixture, and mix until just combined. 3.Using a 11/2-inch ice cream scoop, drop dough onto baking sheets lined with parchment paper, spacing about 2 inches apart.Sprinkle with additional sanding sugar (I use cinnamon sugar). Bake until edges are firm, 10 to 12 minutes. Let cool on sheets on wire racks. Cookies can be stored in an airtight container up to 2 days.