Mix together brown sugar, cinnamon, and pecans; set aside. Cream butter, sugar and eggs together. Fold in sour cream & vanilla. Fold in flour, baking powder and salt.
Spoon 1/3 of the batter into a greased and floured bundt pan. Sprinkle on ½ of the brown sugar cinnamon mixture. Spoon another 1/3 of the batter on top then sprinkle on remaining brown sugar cinnamon mixture. Cover with remaining 1/3 of batter.
Bake at 350° for 60 minutes. Cool completely before removing from pan.