Heat the oven to 356°F (180 °C). Grease the muffin tray or put paper cups in the openings. Sift the flour with the baking soda and baking powder, then mix in a bowl with the cocoa, sugar and salt. In another bowl, using a fork (not a mixer or blender), beat the egg, add the oil and pureed bananas.
To this mixture, add the dry mixture and stir again with fork (but not too much), about 10-15 times. Pour in the chocolate chips and stir the mixture again lightly. The dough is now ready.
Distribute the dough into the muffin tray, being careful not to fill more than 2/3 of the volume of the cups. Bake 20-25 minutes, then remove from the oven and refrigerate at least 5 minutes before removing them from the tray.