Cream the butter and sugar together in a medium-large mixing bowl. Beat in the vanilla and egg, and then mix/knead in the cocoa and flour until the mixture comes together into a soft dough. If you do it in the electric mixer, use the paddle attachment to mix, and it should look something like a stiff chocolate frosting.

Cover the dough with plastic and refrigerate at least 2 hours, or overnight, till cold.

Remove the dough from the fridge, knead to soften slightly, and roll out on a surface dusted with flour. Keep the dough from sticking by periodically lifting the dough off of your work surface to dust more flour underneath. Rotate the dough regularly to keep it from sticking too much. You will want it about ¼-inch thick by the time you are done.

Tip: I usually roll the dough a couple of times in each direction, and then lift it or move it to dust with flour underneath. Repeat this until you reach the desired thickness.

Lift the cookies onto parchment or wax paper lined cookie sheets. Collect the scraps of dough from between the cookies into a ball, re-roll, and cut, the same as before. Keep repeating this method until you have the dough used up.

Tip: When you get down to the last little bit, I usually just roll the rest of the dough into little balls and flatten them with a fork or my fingers, and then bake them like that.

Bake at 350 degrees F (or 170 degrees C) for 8-12 minutes or until just golden around the edges of some of the cookies. Cool on wire racks.

In a small, heat proof bowl, melt the chocolate in the microwave for 15 seconds at a time, stirring after each, until smooth. Transfer to a piping bag or squeeze bottle, and drizzle the cookies (over parchment paper) with chocolate. Allow to set until cold before storing.