Preheat oven to 350º. In a 9 inch round cake pan bake pecans in a single layer 8 to 10 minutes or until toasted and fragrant, stirring once. Empty pecans from pan and set aside. Place brown sugar, ¼ cup of the butter and cinnamon into the 9 inch round cake pan. Put back into oven until butter is melted and mixture is smooth, stirring occasionally. Remove from oven, stir in rum. Cut bananas diagonally into ¼ inch thick slices and arrange in concentric circles over brown sugar mixture. Place pecans over bananas. Place remaining ½ cup butter, sour cream and sugar in a large bowl and beat at medium speed until light and fluffy. Add eggs one at a time, beating well after each addition. Beat in vanilla. In a medium bowl stir together flour, baking powder, baking soda and salt. At low speed, beat in flour mixture alternating with sour cream mixture, beginning and ending with flour mixture. Spoon and gently spread batter over bananas. Bake 40 to 50 minutes or until cake is golden brown and toothpick inserted in center comes out clean. Cool in pan on wire rack 15 minute. Run small knife around edge of cake then carefully invert cake onto serving plate. Serve warm.