Beat the butter and sugar with a mixer in a large pot. Add egg and mashed bananas. In a separate pot put the other products and mix them, then add them (3 times) to the sugar, the butter, egg and bananas not stop beating with mixer until a homogeneous dough. Spoon take the dough and pour on a buttered baking sheet, so as to form balls that should spread to get the desired type of cookie. Bake at 180 C 10-15 minutes or until edges of cookies become golden brown. Allow cookies to cool completely, then put them in a box with a lid or plate, which you can cover with plastic foil. The cookies are delicious the next day.