3/4 cup whole, shelled, unsalted pistachios
1 cup unbleached all-purpose flour
1 teaspoon baking powder
1/4 teaspoon kosher salt
5 tablespoons unsalted butter
6 tablespoons unsweetened cocoa powder
1 cup granulated sugar
1 large egg
1 teaspoon pure vanilla extract
1 tablespoon golden rum
Grated zest of 1/2 a large orange
1 to 1 1/2 cups of confectioner's sugar for rolling
1. Using a sharp knife, coarsely chop the pistachios and set aside. In a medium bowl, whisk the flour, baking powder and salt together and set aside.
2. Melt the butter, but don't let it boil, and place it in the bowl of an electric mixer. Add the cocoa powder and mix on medium speed to thoroughly combine the ingredients. Beat in the granulated sugar well, then beat in the egg. Scrape down the sides of the bowl, and then beat in the vanilla extract, rum and orange zest.
3. On low speed, beat in the flour mixture halfway, then add the pistachios, beating on low speed to combine the ingredients and form a soft dough. Switch to medium speed and beat for about 30 seconds to strengthen the dough and thoroughly incorporate the dry ingredients. Scrape the dough onto a sheet of plastic and wrap to form a neat package. Chill the dough for at least 4 hours or overnight.
4. When you are ready to bake the cookies, remove the dough from the refrigerator to slightly soften it while you preheat the oven to 325°F and position the racks to the center of the oven. Spray two cookie sheets or rimmed sheet pans lightly with non-stick cooking spray and line them with parchment paper. Place the confectioner's sugar in a shallow bowl.
5. Break off small pieces of dough and roll them in the palm of your hands to form 1/2 to 3/4-inch balls. You can dust your hands with a bit of confectioner's sugar if the dough sticks. Roll the balls in the confectioner's sugar to generously coat them. Place the cookies on the prepared pans, spacing them about an inch apart.
6. Bake the cookies for 8 to 10 minutes, rotating the cookie sheets halfway through the baking time to ensure even baking. Allow the cookies to cool on the sheets for about a minute to let them firm up, and then use a spatula to gently transfer them to rack to cool completely. Store the cookies in an airtight container for up to a week.