Procedure:
1. Preheat oven to 350 degrees F. Butter and flour a 10-inch Bundt pan (12-cup capacity). Position rack in the lower third of the oven.
2. Place the nuts, brown sugar, and cinnamon in the basket of a food processor fitted with the steel blade. Pulse 6 to 8 times or until the nuts are chopped medium and the ingredients are combined. Do not over process. Set aside.
3. Sift together the flour, baking powder, baking soda and salt in a triple sifter. Set aside.
4. Cream the butter on medium-low speed in the large bowl of an electric mixer. Increase the speed to medium-high and beat until smooth and light in color, about 1-1/2 to 2 minutes. Add the sugar, 1 tablespoon at a time, taking about 6 to 8 minutes to blend it in well. Add the eggs, 1 at a time, scraping the sides of the bowl as necessary. Beat for about 1 minute longer. Blend in the vanilla.
5. On low speed, add the dry ingredients alternating with the sour cream, beginning and ending with the flour (3 parts flour/2 parts sour cream). Mix only until incorporated after each addition. Scrape the side of the bowl and mix for 10 seconds longer.
6. Spoon about 1/3 of the batter into the Bundt pan, smoothing the surface with the back of a tablespoon. Using the tip of a teaspoon or your fingertips, break apart the filling and distribute ½ of the filling evenly over the batter.
7. Spoon 1/2 of the remaining batter into the pan, then the remaining filling. Cover with the remaining batter, spreading the batter evenly from the center out. It is important that the last layer of filling be covered with the batter. Smooth the surface.
8. Center the pan on the rack and bake for 60 to 65 minutes or until the cake is golden brown on top and it begins to come away from the sides of the pan. A toothpick inserted into the center should come out clean. Cool the cake on a rack for 10 to 15 minutes. Invert and gently remove the pan. Before serving, dust the top with confectioners sugar.
