Step 1

Combine the butter and sugar in the bowl of a large stand mixer fitted with a paddle attachment, and cream until pale and fluffy. Scrape down the bowl, and add the egg and continue beating until the egg is incorporate and the mixture lightens in color. Add the cocoa powder and beat until there are no lumps. Finally, fold through the flour and salt until it is all incorporated. The dough will be very soft.

Step 2

Scrape the dough out onto a piece of parchment paper. Add a second sheet of paper on top, and roll out the dough between the two sheets until it is a rectangle about 1/4-inch thick. Place the dough on a tray and freeze it for 30 minutes, or refrigerate it for 1-2 hours, until firm.

Step 3

Preheat the oven to 350 F (180 C). Line two baking trays with parchment paper.

Step 4

Cut the chilled dough into 28 small 1 1/4 in x 2 1/2 in rectangles. Place them in evenly spaced intervals on the baking sheets and bake for 10 minutes. Let the cookies cool completely at room temperature.

Step 5

Cream the butter until soft, then sift in the remaining ingredients and beat until light and fluffy. Spread a heaping teaspoon of filling on half of the cookies, or transfer the frosting to a piping bag and pipe an even layer of filling on half of the cookies. Top with the remaining cookies, then put in the refrigerator to chill while you make the coating.

Step 6

For the coating, place the chocolate and coconut oil in a heat-proof bowl and melt them together in the microwave in 30-second bursts, stirring after every 30 seconds to prevent overheating. Once the chocolate is mostly melted, remove and stir gently until smooth.

Step 7

Using a fork or dipping tools, dip a chilled cookie in the melted chocolate and place it back on the baking sheet. If you want to create a wavy pattern on top of the cookies, lightly press the tines of the fork or dipping tool to the top while the chocolate is still wet. Repeat until all of the cookies are dipped. Chill in the refrigerator, then devour!