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 a 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 (dough will still be sticky). Drop a one-inch ball of dough onto cookie sheets 2-inches apart (about 1 ½ Tbsp).
Bake at 350 degrees for 10-13 minutes or until the edges are brown.
