Vanilla Cake:

1. Preheat oven to 350°F (177°C).
2. In a large bowl, combine cake mix, eggs, oil, buttermilk, and vanilla. Mix until you have a thick batter.

Cinnamon Swirl:

1. In a small bowl, combine brown sugar, flour, cinnamon, and melted butter. Stir until combined.

Cake Assembly and Baking:

1. Grease a bundt pan with nonstick spray.
2. Pour half of the cake batter into the pan. Spoon over half of the cinnamon swirl mixture and swirl with a toothpick.
3. Pour the remaining batter on top, then the remaining cinnamon swirl. Swirl again.
4. Bake for 40-45 minutes, or until a toothpick inserted comes out with a few moist crumbs.
5. Cool in the pan for 15 minutes, then invert onto a serving plate and cool completely.

Cream Cheese Glaze:

1. Combine softened cream cheese and butter in a bowl and mix until smooth.
2. Add vanilla extract and powdered sugar, and mix until you have a frosting consistency.
3. If the frosting is too thick, add a tablespoon of milk or microwave for 20 seconds.

Frost and Decorate:

1. Add the cream cheese glaze to a piping (or zipper) bag and pipe onto the cooled cake in a zigzag pattern.
2. Combine cinnamon and sugar in a small bowl. Sprinkle over the glaze.
3. Serve immediately or store in the refrigerator for up to 4 days.