1. Preheat the oven to 350°F. Grease a 9 or 10" tube pan with removable bottom, or a 9" x 13" pan.
2. For the filling/topping: In a small bowl, combine the walnuts, cinnamon, and sugar; set aside.
3. For the batter: In a medium bowl, whisk together the flour, baking powder, baking soda and salt. Set aside.
4. In a large bowl, beat together the butter, oil, and sugar until well mixed. Add th eggs, one at a time, beating well after each addition.
5. Reduce the mixer speed to low, and gradually beat in the flour mixture, sour cream and vanilla. Scrape the sides and bottom of the bowl, and beat for 30 seconds more.
6. Spoon half of the batter into the pan, and sprinkle with half the nut mixture.
7. Spoon the remaining batter into the pan, and sprinkle with the rest of the nut mixture.
8) Bake the cake for 50 to 60 minutes, or until it tests done. If you're using a 9" x 13" pan, bake for 35 to 40 minutes. Remove from the oven, cut in wedges and serve warm.
Yield: about 16 servings.