Make the Cake: 

1. Preheat your oven to 350ºF and grease a 9×13″ baking dish. Set it aside. 
2. Combine your cinnamon and brown sugar, and nutmeg in a small bowl and set that aside too.
3. In a large mixing bowl, using a hand mixer – or your arms if your strength and endurance are up to it – beat together the cake mix, eggs, butter and sour cream just until smooth and fluffy.
4. Pour half of that batter into your prepared dish, then sprinkle the brown sugar mixture over it, evenly. Cover it well. 
5. Pour the remaining batter over the top of the brown sugar and spread to cover it. I usually spoon dollops of batter all over the top of the brown sugar, then smooth it out with a spatula. Makes it easier.
6. Bake in the oven for about 30 minutes. Use a cake tester or toothpick if you need it – it should be clean after sticking it in and pulling it straight back out of the center of the cake. If it looks wet, keep baking. 

Make the Glaze: 

1. Combine the sugar, milk and vanilla extract in a small bowl. Whisk until there are no more lumps. It may take some time and effort but you’ll get there, I promise. 
2. Pour the glaze over the cake as soon as you pull it from the oven, and spread it over the entire top.