In a large bowl, combine flour, black cocoa powder, and salt.

Add your butter and work in with your hands or a fork until mixture has small clumps.

Add your egg yolk and work into a dough, just until combined. Wrap and chill for at least 30 minutes.

Preheat oven to 350°F. Remove dough from fridge and let rest for 15 minutes.

Cut even rectangles with a cookie cutter or a ruler and knife (about 2” x 4”) and transfer to a piece of parchment paper with a spatula.

Press dough scraps into a ball and roll out again to the same thickness, cutting more cookies until you have a total of 10-12.

Chill dough for 5 minutes in the fridge or freezer. Then, using a chopstick or dowel, press a vertical bisecting line into each rectangle (not pushing all the way through, just enough to indent).

Then, repeat pressing lines into each cookie horizontally, 3 times equally to form 8 chocolate “square” shapes on each.

Chill cookies for 10 minutes in the freezer before baking to keep from spreading. Then, bake for 15 minutes.

Remove cookies from oven and press your chopstick or dowel into the cookies once again with less pressure to reaffirm the chocolate bar lines.

Let cookies chill for a few minutes, then transfer carefully with a spatula to a wire cookie rack. Let rest again for at least 30 minutes.

Next, place your chopped chocolate bar or chocolate chips in a microwave-safe bowl. Microwave on half power for 2 minutes until starting to melt and stir.

Then, continue microwaving in 30 second bursts on full power, stirring each time, until completely melted.

Add your coconut oil and whisk to combine. Make sure the oil melts completely.

Pour your chocolate coating equally onto each cookie, covering the tops completely. Place a baking sheet lined with parchment paper under the wire rack to collect chocolate discard.

Then, transfer cookies to fridge to set completely and serve.