01 - Preheat oven to 350°F. Lightly grease a 9x13-inch baking dish to prevent sticking.
02 - In a large mixing bowl, blend cake mix, eggs, milk, vegetable oil, and vanilla extract with a mixer for about 2 minutes until batter is smooth. Pour evenly into the greased dish and smooth the surface.
03 - Place the baking dish in the oven and bake for 25 to 30 minutes, or until a toothpick inserted in the center emerges clean.
04 - While cake bakes, combine brown sugar and cinnamon in a small bowl. Stir in melted butter until a thick paste forms.
05 - Once baked, remove cake from the oven. While hot, use the handle of a wooden spoon to create holes approximately 1 inch apart across the surface.
06 - Spoon or drizzle cinnamon filling over the cake, ensuring mixture seeps fully into the holes. Allow cake to cool completely in the dish.
07 - In a mixing bowl, beat cream cheese and softened butter together until smooth. Add powdered sugar, milk, and vanilla extract; continue beating until frosting is creamy.
08 - Spread cream cheese frosting evenly over the cooled cake. Slice into pieces and serve as desired.