Prepare Crumb Topping: In bowl mix pecans, brown sugar, flour and cinnamon until well blended. Add butter until mixture resembles crumbs.
Prepare Cake: Preheat oven to 350 degrees F. Grease 9" Springform pan; dust with flour. In small bowl mix flour, baking powder, baking soda and salt, set aside.
In large bowl with mixer on medium speed, beat sugar, butter and vanilla 5-6 minutes or until mixture is fluffy. Reduce speed to low; add eggs one at a time, beating well after each addition. With mixer on low speed, add flour mixture alternately with sour cream.
Pour batter into prepared pan. Sprinkle with crumb topping and gently press into batter. Bake 40-45 minutes, until toothpick inserted in center of cake comes out clean. To serve warm: cool cake in pan on wire rack 15 minutes. With a knife loosen cake from side of pan. Cool additional 30 minutes.