Preheat oven to 350°. In a large bowl, mix flour, baking powder, baking soda and salt. In another bowl, beat sugar, sour cream, eggs and vanilla until well blended. Stir into flour mixture just until moistened. Fold in apples and 1 cup pecans.
Transfer to a greased 9×5-in. loaf pan. Bake 50-55 minutes or until a toothpick inserted in center comes out clean. Cool in pan 10 minutes. Remove to a wire rack to cool completely.
In a small saucepan, combine butter and brown sugar. Bring to a boil, stirring constantly to dissolve sugar; boil 1 minute. Spoon over bread. Sprinkle with remaining pecans; let stand until set.