Preheat oven to 325°F. For the Streusel Topping, mix flour, brown sugar and cinnamon in medium bowl. Cut in cold butter with pastry blender or 2 knives until mixture resembles coarse crumbs. Stir in pecans. Set aside.
For the Cake, beat softened butter, granulated sugar and sour cream in large bowl with electric mixer on medium speed until light and fluffy. Add eggs, 1 at a time, beating well after each addition. Mix in vanilla. Gradually beat in flour and baking soda on low speed until well mixed.
Spoon 1/2 of the Streusel Topping into greased and floured 12-cup Bundt pan. Spoon 1/2 of the batter over top. Repeat layers.
Bake 1 hour or until toothpick inserted in center comes out clean. Cool in pan 10 minutes. Remove from pan. Cool completely on wire rack. Sprinkle with confectioners' sugar, if desired.