Preheat oven to 350 degrees F. Grease and flour a 10 inch tube pan.
Prepare nut mixture first. Stir together nuts, brown sugar and cinnamon. Set aside.
Sift together the already-sifted cake flour, baking powder and salt and set the flour mixture aside.
In a large mixing bowl, cream the butter and sugar using high speed of an electric mixer for about 2 minutes. Add the eggs one at a time, beating for 30 seconds after each egg. Beat in the vanilla, then fold in the sour cream. Add the flour mixture and stir with a mixing spoon (do not beat) into the batter, mixing until incorporated.
Spoon about half of the batter into the greased/sprayed pan, then sprinkle a light ring of nut mixture over the batter. Spoon remaining batter over ring, then spoon remaining topping decoratively over top. Bake for 50 minutes to an hour. The Junior League baked theirs for one hour, but mine was most definitely done in 50 minutes.
Let cool for 10 minutes in pan. Remove from pan by inverting onto a flat dish, then inverting again onto a rack to finish cooling. When you are ready to serve it, you can transfer it to a nice plate.