combine brown sugar, cinnamon and walnuts in a small bowl -- topping. Set aside.
2
spray 9-inch tube ban with cooking spray. Preheat oven to 350 degrees.
3
whisk together flour, baking powder, baking soda and salt. Set aside
4
cream butter and sugar. mix in eggs, one at a time, until blended smooth. Add sour cream and vanilla. Beat until smooth.
5
add flour mixture and beat slowly until combined.
6
spoon half batter into prepared pan, spread evenly. sprinkle 2/3 of topping, then spread remaining batter.
7
cook 8 minutes, then sprinkle remaining topping. Continue baking for 25 to 30 minutes until cake is firm to touch (careful not to burn yourself on the topping!).