Preheat the oven to 325 degrees and spray a 9x13 baking pan with nonstick cooking spray.
In a medium bowl add the cake mix, eggs, milk and vegetable oil and using a hand mixer min for 1-2 minutes. Pour the cake batter into the prepared baking pan.
In a small bowl add the butter, brown sugar, flour, and cinnamon and mix until combined.
Add dollops of the mixture onto the cake batter. Using a butter knife makes swirls throughout the cake batter. Don't over-stir the batter, you want streaks of cinnamon throughout.
Bake for 30-35 minutes or until a toothpick comes out clean. Remove from the oven and let cool for at least an hour.
Cream Cheese Frosting
In a medium bowl add the softened cream cheese, powdered sugar, and vanilla and using a hand mixer, mix until combined. Add in the milk according to your desired consistency. You can leave it out if you prefer a thicker frosting.
Once the cake as cooled spread the frosting over the top and serve!
Video
Notes
I used Super Moist but any brand cake mix will work.