Combine yellow cake mix, eggs, sour cream, and vegetable oil. Mix together and pour half in a 9x13 inch pan. Mix brown sugar and cinnamon. Sprinkle over half of batter in pan. Pour rest of batter over brown sugar mixture. Bake at 350 degrees for 30-35 minutes. Topping: combine powdered sugar, vanilla and milk. While cake is warm poke holes in cake with toothpick. Pour topping over cake.