01 - Preheat oven to 350°F. Grease a 9x13-inch baking dish with nonstick spray or butter.
02 - In a large mixing bowl, combine cake mix, eggs, milk, vegetable oil, and vanilla extract. Beat with a mixer on medium speed until smooth, about 2 minutes. Pour the batter into the prepared baking dish and spread evenly.
03 - Transfer to the oven and bake for 25 to 30 minutes, or until a toothpick inserted into the center comes out clean.
04 - While the cake bakes, combine brown sugar and ground cinnamon in a small bowl. Stir in melted butter until a thick paste forms.
05 - Remove cake from oven and immediately use the handle of a wooden spoon to poke holes over the surface, spacing about 1 inch apart. Spoon or drizzle the cinnamon filling over the warm cake, letting it seep into the holes.
06 - Allow the cake to cool completely in the baking dish.
07 - In a clean mixing bowl, beat the softened cream cheese and butter together until smooth. Add powdered sugar, milk, and vanilla extract, and beat until creamy.
08 - Spread the cream cheese frosting evenly over the cooled cake. Slice into squares and serve.