Preheat the oven to 350 degrees F.
Prepare the dry cake mix, eggs, water and oil with a hand mixer. Beat until smooth, Blend in the sour cream. In a separate bowl, combine the brown sugar and cinnamon. Spray a bundt pan with cooking spray. Pour 1/2 of the cake batter in the bundt pan. Spread the brown sugar/cinnamon mixture over the batter. Top with remaining cake batter. Bake for 25-30 minutes. Cook for about 15 minutes before inverting onto a platter.
The Glaze: Mix together 1/2 cup confectioners sugar, 1 t. vanilla and 2 t. milk. Stir well, then drizzle glaze over warm cake!