Mix baking soda into sour cream and let sit for 1 hour.
Mix together butter, sugar, eggs, vanilla, flour and baking powder. Add sour cream mixture.
In a separate bowl mix brown sugar, cinnamon and chopped nuts.
Pour half of the batter into a coffee cake pan and sprinkle half of the nut mixture evenly over the batter. Spread the other half of the batter evenly over the first layer and sprinkle the other half of the nut mixture over top of the cake.
Bake at 350℉ for 55 - 60 minutes.
Run a knife around the outside of the cake, around the hole in the cake and remove from pan. Run a knife around the bottom of the pan and life the cake from the cone. Slice and serve.