These cookies are traditionally made for the Jewish holiday of Purim, and the traditional filling is made of prunes or poppy seeds. However, I've found these are tremendously popular anytime, and can be spiffed up by using any kind of jelly, jam or preserves as filling. This recipe is lower in fat than my normal recipe (for the full-fat version, replace the banana with another stick of butter and the low-fat yogurt with sour cream). Enjoy! I always get lots of great comments on these.