Mix cake mix, eggs, oil and sour cream together. Beat well. Pour half of mixture in a 13 x 9-inch, lightly greased pan. Mix brown sugar and cinnamon together. Sprinkle over batter in pan. Spoon rest of batter around on top of mixture. Bake at 325 degrees for 50 to 60 minutes. Punch holes in cake. Mix powdered sugar, milk and vanilla together. Pour over cake. If you like more icing on your “Honey Bun”, double up on the powdered sugar, milk and vanilla mixture and use as much as you like.