Before starting, preheat oven to 325 degrees F and line a 6inch cake pan with parchment paper. Cut out 12 strips (0.5 x 4.0 inches) of plastic sheet with the edges trimmed to triangular points.
Combine 4 ounces chocolate and butter in a bowl and microwave for about 1 minute at 500 watts until chocolate has melted.
In a separate bowl, cream together the eggs and sugar.
Add the chocolate/butter mixture and cream to the egg mixture and mix well.
Fold in the flour and cocoa powder until just combined.
Pour into a cake pan and bake for 40 minutes at 325 degrees F.
To make the chocolate ribbons, pour the melted chocolate over the strips of plastic sheet. Once the chocolate is dry but still soft and pliable, lift off the strips of plastic and carefully mold them so that the ends meet each other.
Remove the plastic strips from the chocolate ribbons and arrange on top of the cake.