Combine brown sugar, walnust and cinnamon and mix together.
Spray a bundt pan and preheat over to 350 degrees.
Sift together flour, baking powder, baking soda and salt; set aside. Using electric mixture beat sugar and butter until well blended. Beat in eggs and vanilla. Add flour mixture until combined. Mix in sour cream.
Spoon half of batter into prepared pan. Sprinkle nut mixture over the batter. Spoon remaining batter over nut mixture.
Bake until tester comes out clean, about 50-60 minutes.