Over barely simmering water, melt chocolate and butter. Over boiling water, whisk eggs and sugar until 165 degrees and thickened. With electric mixer, whisk eggs to ribbon stage. Fold in chocolate. Sift cocoa and fold in. Refrigerate for 1 hour. Butter and layer 2 sheets of filo. Fold into quarters. Place 1/6th of cake batter in center and pull up sides of filo to wrap. Flip over into 2 1/4-inch entremet ring, or individual foil muffin pan. Repeat with other batter to make 6. Refrigerate for 30 minutes. Preheat oven to 400 degrees. Bake cakes for 12 minutes until browned. Invert onto platter and serve hot.