Mix the flour, baking soda, baking powder, cocoa and salt (dry mixture). Melt in a very low heat the butter in a bulky court and after removing from heat, add sugar, add them puree bananas, beaten egg and vanilla in advance and stir until homogeneous. Gradually add the dry mixture and finally the grated chocolate. Confuse well. Take a tablespoon of the mixture and place on greased baking pan, you can customize mild cookie. Bake about 15 minutes in a preheated 180C degrees. After removing from the oven, leave cookies 2 minutes in the tray to relax and then move the plate.