Preheat your oven to 300 degrees F. Coat an 8-inch round cake pan with non-stick spray or butter.
With an electric mixer, beat the butter until creamy. Add the flour, sugar and cocoa - and mix until combined.
Chill the dough in refrigerator for 10 minutes. Pat down the dough into the pan. Press down the edges with tines of floured fork.
Bake until firm, about 30 minutes. Immediately score into wedges. Turn out pan and break wedges apart. Let cool on a wire rack.