Preheat the oven to 350 degrees. Spray a bundt pan with cooking spray really well, then coat the pan with sugar.
With a hand mixer, combine the cake mix, pudding, flour, eggs, water, and oil in a large bowl. Stir in the chocolate chips (optional).
Spoon into the bundt pan and bake for 45-55 minutes. My oven bakes really slow, so mine always takes longer, but start checking around 45 minutes, just to make sure. Cake is done when a toothpick comes out clean.
Cool for 10-15 minutes, then turn out onto a cake plate. While it's cooling, make the frosting!
To make the frosting: Measure the powdered sugar into a large mixing bowl. In a large glass measuring cup, or glass bowl (microwave safe), melt the butter, cocoa, and 2 tablespoons of the milk until it comes to a boil. Stir well, then add to the powdered sugar. Add the vanilla and the rest of the milk, beating with a wooden spoon until the consistency is smooth. Add a little more milk if necessary.
I like my frosting to be a little thicker on the cake, so once I have the frosting consistency they way I like it, I microwave it for about 10 seconds. Then I can easily spoon the frosting over the cake, and it will go right back to the consistency I started with. If you like it a little thinner, then add a little more milk--then you won't have to microwave it.