Preheat oven to 350°F Combine butter and 1 cup sugar in a bowl and beat with an electric mixer until light and fluffy. Add eggs one at a time, mixing thoroughly after each addition. Stir in bananas, vanilla and sour cream.
Sift flour and next 3 ingredients together in a bowl. Fold into butter mixture until just blended.
Combine nuts, cinnamon and remaining granulated sugar in another bowl. Sprinkle half of nut mixture into a buttered and floured tube or bundt pan. Add half the batter. Sprinkle with remaining nut mixture and cover with remaining batter.
Bake 45-50 minutes until a tester comes out clean when inserted in center. Invert pan and cool. Sprinkle with powdered sugar before serving.