Preheat the oven to 350°F (175°C). Generously grease a 9-by-13-inch baking pan with cooking spray. Prepare the white cake mix according to the package instructions. Pour the batter into the greased pan and bake for approximately 20 minutes, or until a toothpick inserted into the center of the cake comes out clean. Allow the cake to cool slightly for 10 minutes before proceeding.

While the cake is baking, combine the sweetened condensed milk, melted butter, brown sugar, ground cinnamon, and salt in a medium mixing bowl. Whisk until the mixture is smooth and fully combined. Set aside.

Using the handle of a wooden spoon or similar utensil, poke holes evenly across the surface of the slightly cooled cake, spacing them about one inch apart. Pour the cinnamon filling over the cake, using a spatula to help press the mixture into the holes for even distribution. Let the cake rest as the filling soaks in.

In a large mixing bowl, whip the heavy cream using an electric mixer until stiff peaks form. In a separate bowl, beat the softened cream cheese and butter together until smooth and lump-free. Add the powdered sugar, vanilla extract, and salt, and beat until creamy and well combined. Gently fold the whipped cream into the cream cheese mixture until fully incorporated.

Spread the prepared frosting evenly over the top of the cake. For best results, refrigerate the cake for at least 20 minutes before serving to allow the frosting to set. Serve chilled or at room temperature as desired.