1. Prepare Pecan Streusel: Combine first 3 ingredients in a bowl. Cut in butter with a pastry blender or fork until mixture resembles small peas. Stir in 3/4 cup pecans.
2. Prepare Pound Cake Batter: Preheat oven to 350°. Bake 1 cup pecans in a single layer in a shallow pan 5 to 7 minutes or until lightly toasted and fragrant, stirring halfway through. Cool 20 minutes. Reduce oven temperature to 325°.
3. Beat butter at medium speed with a heavy-duty electric stand mixer until creamy. Gradually add granulated sugar, beating until light and fluffy. Add eggs, 1 at a time, beating just until blended after each addition.
4. Stir together flour and baking soda; add to butter mixture alternately with sour cream, beginning and ending with flour mixture. Beat at low speed just until blended after each addition. Stir in vanilla.
5. Pour half of batter into a greased and floured 10-inch (12-cup) tube pan. Stir together toasted pecans, brown sugar, and cinnamon; sprinkle over batter. Spoon remaining batter over pecan mixture; sprinkle with Pecan Streusel.
6. Bake at 325° for 1 hour and 20 minutes to 1 hour and 30 minutes or until a long wooden pick inserted in center comes out clean. Cool in pan on a wire rack 10 to 15 minutes; remove from pan to wire rack, and cool completely (about 1 hour).