Preheat oven 375º
1. Remove 1/2 c dry cake mix and set aside.
2. Beat remaining dry cake mix, butter, eggs and sour cream in a large bowl on medium speed for 2 minutes.
3. Spread 1/2 cake batter into a generously greased bottom only of13x9 pan.
4. Mix reserved dry cake mix, brown sugar, pecans and cinnamon.
5. Sprinkle over batter in cake pan.
6. Drop spoonfuls of remaining batter in cake pan and spread carefully. Make sure all topping is covered.
7. Bake for 30-35 minutes or until deep golden brown and cake springs back when touched lightly in the center.
8. Stir powdered sugar, milk and vanilla until thin enough to drizzle, stirring in additional milk 1 tsp at a time.
9. Poke top of warm cake several times with fork, spread glaze over top of cake. Cool competently, about 1 hour. Store covered.