In a bowl, beat cake mix, oil, eggs and sour cream until all combined. About 2 minutes. Spread half of the batter in pan evenly.
In small bowl, add the brown sugar and cinnamon. Sprinkle over the batter in the pan. Spread the remaining batter evenly over sugar cinnamon mix and even the surface.
Bake for 45 - 50 minutes or the cake is a golden brown.
For the glaze, in a small bowl, add the melted butter, powdered sugar, milk and vanilla and stir until it is a think consistency.
Use a fork or skewer and prick holes in the surface of the cake whilst it is still warm. then spread the glaze over cake. Allow to cool before slicing.