Melt 1/4 cup better in 8 inch square baking dish; blend in brown sugar and cinnamon. Sprinkle pecans over brown sugar; place apple slices in single layer over nuts. Stir baking soda into sour cream and allow to stand 10 minutes. Cream remaining 1/2 cup butter; add eggs and beat thoroughly. Stir flour, sugar and baking powder together. Add dry ingredients and sour cream alternately to creamed mixture, beginning and ending with dry ingredients. Pour over apples; bake at 350~ for 45 to 50 minutes or until toothpick inserted in center comes out clean. Cool in dish 10 minutes; invert onto serving dish. ----