Black Cocoa Shortbread Cookies

1. In the bowl of your stand mixer fitted with a paddle attachment, mix room temperature butter and vanilla until light and fluffy. About 2 minutes on medium. Then add sifted confectioners' sugar and mix until incorporated. You can also use a hand-held mixer.
2. Next, sift in flour, black cocoa and salt. On the lowest setting, mix until just combined. Do not overmix.
3. Transfer dough to cling wrap and chill for at least 1 hour. I like to shape the dough into a rectangle, about 1-inch (2.5 cm) thickness to make it easier to roll out later.
4. Roll your dough out to 1/8 inch (3.1 mm) thickness. Lightly dip your cookie cutter into cocoa powder and cut out your cookies. With a metal spatula, carefully transfer the cookies to 2 to 3 lined baking trays, placing them 2 inches apart. Gather the scraps, reroll and cut out more cookies. I used a 2.5 inch (6.3 cm) fluted cutter and got 32 cookies, giving me total of 16 sandwiches. If at any point the dough gets too warm from handling, don't fret, pop it back in the fridge for 15 minutes or so to firm up!
5. With a round 1-inch (2.5 cm) cutter, punch a hole in the center of 16 cookies, while leaving the other 16 whole. Place the trays in the freezer for 20 minutes. This is a very important step and cannot be skipped!
6. While it's freezing, set a rack in the center of your oven and preheat to 350ºF (176ºC).
7. Bake for 10 minute, one tray one tray at a time (keep the other trays in the freezer or fridge until the oven is available). Allow baked cookies to sit on the tray for about 3 minutes, then transfer to a wire rack to cool completely.
8. Combine chocolate SunButter and confectioners' sugar. Once the cookies are cooled, lightly sift confectioners' sugar on top of each cookie. Flip the bottom cookies over and spread about 1 1/2 teaspoons of the chocolate SunButter mixture, stopping 1/8 inch from the edge. Place the cookie (with the hole) on top of the chocolate filling and press down lightly. Serve and Enjoy!!