Heat the butter in a small saute pan until it turns brown and smells nutty. Remove from heat and add the white and brown sugars. Let sit for about 5 minutes to cool. Pour into a large mixing bowl and add the egg and vanilla. Mix in banana and sour cream. In separate bowl, combine flour, baking soda, baking powder and salt. Fold into banana mixture. Fold in chocolate chips and nuts, if desired. Choose your own additions, you could also use raisins, toffee bits, pecans, etc. Refrigerate dough for at least 30 minutes. Drop a one inch ball of dough onto cookie sheets 2-inches apart and bake at 350 degrees for 10-13 minutes or until edges are brown.