Sift together flour, baking soda, baking powder, and salt.  Set aside.  Work butter until soft, then work in sugar a little at a time until smooth.  Beat in eggs one at a time, and add the vanilla, grated lemon rind, and bananas.  Stir in the flour mixture alternately with sour cream. Pour into a greased loaf pan & bake in a preheated 350-degree oven for 1 hour, or until a toothpick comes out clean.  Remove from pan & cool on a rack.  I love mine glazed with a mixture of conf. sugar and a little milk.