Beat eggs with sugar and stirred on a hotplate until thickened (ie . not remain uncooked). Careful not to stick it becomes like an omelet - must be stirred constantly, if strong stove is reduced, and have much patience, especially not stop shaking. When finished - it has become thick as cream, more fluffy and pale - away from heat, put it the butter, cut into pieces and cocoa and stir well, melt the butter. Mix again until change color.