Preheat the oven to 350°F.
Prepare the cake as directed on the cake box. Allow the baked cake to cool until it is just warm.
Poke holes all around the cake using the handle of a wooden spoon or a spatula with the holes spaced about ½ inch apart.
In a medium size heat-safe mixing bowl, add the sweetened condensed milk, 5 tablespoons of butter, brown sugar, cinnamon, and vanilla extract. Microwave on high for 1 minute then stir well. Return the bowl to the microwave and heat for another minute and stir well until the brown sugar is well combined into the glaze.
Pour the glaze evenly over the warm cake.
Add the cream cheese and 1/2 cup butter to a large mixing bowl and beat together with an electric mixer until smooth.
Add the vanilla extract, half & half, and 1/2 cup of the powdered sugar and beat on low speed with the electric mixer until combined. Continue beating the frosting and adding the remaining powdered sugar 1/2 cup at a time until all sugar is combined and the frosting is smooth.
Spread the cream cheese frosting over the cake with a spatula. Sprinkle the top of the cake with additional cinnamon, if desired. Slice the cake into squares and serve.