Legendary Coffee Cake

This is probably my most requested recipe.  I found the recipe originally on allrecipes.com (one of my favorite spots to find new recipes) and altered it a bit to make it healthier and more to my taste.  After a few adaptations, this is what we've got.  It tastes incredible right out of the oven, but you'll find that every day it seems to get better and better as the flavors all blend together into coffee cake goodness.

Legendary Coffee Cake

1 pkg yellow cake mix (or try butter recipe yellow for variety), unprepared
1 cup sour cream
4 eggs
2/3 cup oil
2/3 cup brown sugar, packed
2 tsp cinnamon

1 cup powdered sugar
2 Tbsp milk
1 tsp vanilla

1. Preheat your oven to 350 degrees (F) and grease a tube or bundt cake pan.  I find that a tube pan works best for this recipe because it's easier to get the layers right, but either works great.
2. Combine cake mix, sour cream, eggs, and oil in a large mixing bowl.
3. In a separate, small bowl, combine brown sugar and cinnamon until well-mixed.
4. Pour half of the cake batter into the pan.  Sprinkle with brown sugar mixture until there is a thin layer covering the top of the cake mix.  This should take no more than half of the sugar mixture.  Finished it up by layering the rest of the batter on top and sprinkling it with another layer of brown sugar mixture.  If you end up having extra brown sugar mixture, no worries!  You can just mix it into the glaze when you get to that step.  
5. Bake at 350 degrees for approximately 1 hour or until toothpick comes out clean.
6. Prepare glaze by mixing together powdered sugar, milk, vanilla, and any extra brown sugar mixture (if you had any left over) until well blended.  If you find that you want more glaze, just double the recipe, but I usually find that this works well, since the cake is sweet already.
7. Drizzle glaze over warm cake while still in pan.  Continue cooling cake until ready to serve.  It can be served warm or cool, whichever you prefer.