Preheat the oven to 350 degrees.
Grease a 10-12 cup Bundt pan and set aside.
Combine the ingredients for the Cinnamon Swirl Mixture in a medium bowl; set aside.
Place the beater blade onto a stand mixer, or alternatively you can use a hand-held mixer. Into the mixer bowl, add the cake mix, pudding mix, sugar, and cinnamon. Combine on low for 1 minute.
Add the sour cream, eggs, buttermilk, oil, and vanilla. Mix on medium speed for 2 minutes, stopping halfway to scrape the blade and bowl if needed.
Pour half of the cake batter into the Bundt pan. Evenly sprinkle the Cinnamon Swirl Mixture over the batter. You may have to use your hands, as the mixture sets up slightly. Scrape the remaining batter evenly over your Swirl Mixture. Smooth the top.
Bake in the preheated oven for 40 to 55 minutes, depending on the heating elements in your oven. Adjust the cook time as needed for your oven. Check for doneness at 40 minutes by inserting a toothpick into the cake. You want only a few moist crumbs on the toothpick.
Remove from the oven and cool for 20 minutes.
Invert the cake onto a cake stand or cake plate. Be careful, it is still very hot from the oven.
Allow the cake to completely cool before frosting with the Cream Cheese Glaze.
To make the glaze, put all the ingredients in a medium bowl and blend well with an electric mixer or a stand mixer. Add more heavy cream as needed to pour. If you prefer a thicker glaze that can be spread, adjust the powdered sugar to make a thicker glaze.
Glaze the cake and serve. If not serving immediately, do not glaze the cake until you are ready to serve. Keep the cake covered at room temperature for up to 4 days. Refrigerate any leftover glazed cake for up to 4 days.