Prepare crumb topping- in small bowl, mix pecans, brown sugar, flour, and cinnamon until well blended. With fingertips, work in butter until mixture resembles marbles.
Prepare cake- Preheat oven to 350 degrees. Pam spray a 9-inch spring form pan; dust with flour. On sheet of waxed paper, mix flour, baking powder, baking soda, and salt until combined. In large bowl, with mixer on medium speed, beat sugar, butter, and vanilla 5 to 6 minutes or until mixture is fluffy, occasionally scraping bowl with rubber spatula. Reduce speed to low; add eggs, 1 at a time, beating well after each addition. With mixer on low speed, add flour mixture alternately with sour cream beginning and ending with flour mixture, scraping bowl occasionally until batter is smooth. Pour batter into prepared pan. Sprinkle with crumb topping and gently press into batter. Bake 40-50 minutes, until toothpick inserted in center of cake comes out clean. To serve warm- Cool cake in pan on wire rack 15 minutes.