Cream together butter and sugar. Add eggs, 1 at a time, and vanilla. Sift together flour, baking powder, and baking soda. Add to creamed mixture, alternating with sour cream. Mix together nut mixture: chopped nuts, brown sugar and cinnamon.
Pour half of the cake mixture into a greased and floured tube pan and sprinkle with half of nut mixture. Pour rest of batter in pan and top with balance of nut mixture.
Bake 350°F for about 45 minutes, or until cake tester comes out clean. When cake is removed from pan, turn nut side up and drizzle with the frosting while the cake is still warm.