Heat oven to 325, spray a bundt pan w/ cooking spray. In bowl, combine 1/3 cup butter, walnuts, cinnamon, brown sugar and 1/2 cup flour, mis until crumbly.
In lg bowl combine, flour, baking soda and baking powder. In another bowl, beat butter and sugar until mixed. Add eggs, beat until creamy. Stir in vanilla.
Beat in 1/2 the flour mix, beat 1 min. Beat in sour cream and remaining flour mix. Pour 1/2 of walnut mix into bottom of pan evenly. Pour 2/3 batter over walnut mix. Sprinkle w/ remaining walnut mix then remaining batter. Cook about 50 mins, or until a toothpick inserted in center comes out clean.