In a small bowl, mix together the packed light brown sugar and ground cinnamon until well combined. Set aside.
In a large bowl, whisk together flour, baking powder, baking soda, salt, and cinnamon.
Preheat your oven to 350°F (163°C). Get your bundt pan out, but don’t spray/grease your pan until the batter is ready.*(if you grease it and let it sit, the oil will roll down to the bottom of the pan and make it harder for your cake to release)
In a bowl of a stand size mixer fitted with the paddle attachment, on medium speed, cream together the unsalted butter and cream cheese until smooth and creamy. About 1 minutes
Add the granulated sugar to the butter and cream cheese mixture, beating on medium speed until light and fluffy. About 4 more minutes.
With the mixer on medium speed, add the eggs (one at a time) beating for 30 seconds after each addition. With a rubber spatula, scrape down the sides and bottom of the bowl after each egg is added. Then, stir in the vanilla extract on low speed.
With the mixer on the lowest speed, gradually add a third of the dry ingredients to the wet ingredients, and alternate with half of the buttermilk, making sure to begin and end with the dry ingredients. You should finish by adding the remaining dry ingredients last. Mix until just combined, being careful not to overmix.
Using pam’s cooking spray, and grease a 12 cup bundt cake pan making sure to get into the crack and crevices.
Pour half of the batter into the prepared bundt pan and with the back of a spoon, spread it out evenly across.
Sprinkle the cinnamon mixture evenly over the batter in the pan.
Pour the remaining batter over the cinnamon swirl layer and spread it out evenly.
Use a knife or skewer to gently swirl the batter and cinnamon mixture together, creating a marbled effect.
Bake in the preheated oven for 50-60 minutes, or until a toothpick inserted into the center comes out clean.
Remove the cake from the oven and allow it to cool in the pan for 15 minutes.
After 15 minutes, carefully invert the cake onto a cake board or a cake plate to cool completely. While the cake is cooling, start making the frosting.
For The Cream Cheese Glaze
In the bowl medium size bowl using a hand electric mixer, combine the butter and cream cheese. Cream on medium speed for about two minutes. Scrape down the sides and bottom of the bowl. Beat again for 2 more minutes.
With the mixer on low speed, add the powdered sugar, followed by the vanilla, heavy whipping and salt. Beat on low just until mixed. Then turn the mixer to medium high speed and beat the mixture for 2-3 minutes.
Once the cake is completely cooled, and no longer warm, frost the top.
In a plastic bag or a piping bag and set aside.
Assembly
When the cake has mostly cooled, melt butter in a microwave safe bowl.
While the cake is still slightly warm, use a pastry brush to lightly brush on the melted butter, and then add cinnamon sugar mixture to the top and sides.
If the cream cheese is slightly stiff, place it in the microwave for 7 seconds, and then pour the glaze on the top of the cake and serve!