Preheat the oven to 350F. Line two cookie sheets with parchment paper.
In a medium bowl, whisk together the flour, cocoa and salt until combined. Set aside.
2 ½ cups all purpose flour, ½ cup black cocoa powder, ½ teaspoon fine sea salt
In the bowl of a stand mixer fitted with the paddle attachment, beat together the butter and sugar until thoroughly combined.
1 cup unsalted butter, room temperature, 1 cup granulated sugar
Add the egg, followed by the vanilla extract beating until just combined.
1 large egg, room temperature, 2 teaspoons pure vanilla extract
Scrape down the bowl. With the mixer on low speed, gradually add the flour/cocoa mixture and beat until just combined.
Turn the dough out onto a work surface sprinkled lightly with confectioner's sugar. Pat the dough into a disc shape.
Wrap tightly with plastic wrap and place in the refrigerator for at least 30 minutes.
Place the chilled dough on a work surface that has been lightly sprinkled with flour. Sprinkle the top of the dough and the rolling pin lightly with confectioner's sugar to prevent any sticking.
Roll out the dough to ⅛" - ¼" thick, depending on your preference, rotating the dough as you roll to prevent the dough from sticking.
Cut out desired shapes and place the cookies 2" apart on the cookie sheets.
Place the cookie sheets into the refrigerator for 30 minutes to chill.
Bake the cookies for 12-17 minutes. Rotate the cookie sheets, halfway through baking. You're looking for the cookies to be soft when touched in the center, but fully cooked. Baking the cookies longer will result in a crispier cookie while baking them to just cooked will keep them soft.
Let the cookies cool on the cookie sheets for 10 minutes, before transferring them to a cooling rack to cool completely before decorating.
1 recipe Royal icing