Preheat Oven: Preheat the oven to 356ºF (180ºC) fan-forced. Line a baking sheet with parchment paper and set it aside.
Crush Pecans: In a high-speed food processor or coffee grinder, crush the pecans until they turn into a crumb. Set aside to mix into the dough later.
Combine Dry Ingredients: In a medium-sized mixing bowl, combine the flour, cocoa powder, baking powder, and baking soda. Whisk well and set aside.
Mix Wet Ingredients: In a separate large mixing bowl, using a hand mixer or a stand mixer fitted with the paddle attachment, whisk together the softened butter and sugar for 1 minute until well combined. Scrape down the sides of the bowl.
Add Egg and Vanilla: Add the egg and vanilla extract, and beat for 20 seconds until smooth.
Incorporate Dry Ingredients: Add the flour mixture to the wet ingredients and beat until it begins to form a soft crumbly dough, about 30 seconds. The dough will be crumbly and not a ball of dough.
Add Crushed Pecans & Chill Dough: Mix in the crushed pecans until evenly distributed throughout the dough, then form the mixture into a smooth compact cookie dough. Wrap the dough in cling film and refrigerate for 15 minutes to firm up.
Shape Cookies: Pick up 1 tablespoon (30g) of dough, roll it into a ball, and place it on the prepared tray. Gently press down into a thick disc, ensuring there is a 1-inch gap between each cookie.
Add Whole Pecans: Once all the cookies are formed, press a whole pecan into the middle of each cookie.
Bake: Bake for 10-11 minutes, or until cracks form on the top and the centers are set.
Cool on Tray: Allow the cookies to cool on the baking sheet for 2 minutes before transferring to a wire rack to cool completely. Enjoy!