Preheat oven to 325°F. Prepare fluted tube pan with vegetable pan spray.
In small bowl, combine filling ingredients; set aside.
In medium bowl, combine flour, baking powder, baking soda and salt. In large bowl, beat butter and granulated sugar with electric mixer until light and fluffy. Add eggs, one at a time, mixing well after each. Add vanilla extract; mix well. Add flour mixture alternately with sour cream, beating after each addition until just combined.
Spoon half of batter into prepared pan. Sprinkle evenly with filling. Spoon remaining batter over filling. Using thin knife, drag through batter to swirl cinnamon mixture into filling.
Bake 60-70 minutes or until toothpick inserted in center of cake comes out clean. Cool cake in pan 15 minutes. Remove from pan to cooling grid; cool completely.
In small bowl, stir together confectioners’ sugar and enough milk to drizzling consistency. Drizzle over cooled cake. Sprinkle with additional walnuts.