For Cake: Cream butter and sugar in a large bowl. Add eggs and vanilla. Combine flour, baking soda, and baking powder in a separate bowl. Alternately add flour mixture and sour cream to butter mixture. Beat until fluffy.
For Filling: Combine cinnamon, brown sugar, and pecans in small bowl.
Assembly and Baking: Grease and flour 9x13 baking dish. Pour half of batter into pan and spread evenly. Sprinkle half of filling over batter. Pour and spread remaining batter and sprinkle with remaining filling. Bake for 35 minutes at 350º. While baking, prepare topping.
For Caramel Topping: Melt butter in medium saucepan over moderate heat. Add milk, brown sugar, and pecans and stir 3-4 minutes.
When cake is done, remove from oven and pour caramel mixture over the top, spreading evenly. Broil cake, watching carefully, until caramel topping begins to bubble, about 3 minutes. Let cake cool completely.