Preheat oven to 350°F; lightly grease 2 baking sheets or line them with parchment paper.
In a medium bowl cream together the butter, sugar, baking powder, espresso powder, vanilla and salt. Add the eggs, beating until smooth. Stir in the cocoa powder, then the flour; the dough will be stiff. Mix in the chocolate chips.
Drop by tablespoonfuls onto the prepared baking sheets. Bake for 12 minutes. They will look not quite done in the center. Remove them from the oven and allow them to cool for about 10 minutes. Gently squeeze and shape the cookies into uneven balls to resemble chunks of coal.
Cookies stay fresh at room temperature no longer than a week. They may be frozen.