Step 1: Prepare the Cake: Prepare the cake batter according to the package directions. Pour the batter into a greased and floured 9x13 inch baking pan.
Step 2: Bake the Cake: Bake according to package directions, or until a wooden skewer inserted into the center comes out clean. Let the cake cool completely in the pan.
Step 3: Poke Holes in the Cake: Use a fork or wooden skewer to poke holes all over the surface of the cooled cake. This will allow the milk mixture to penetrate evenly.
Step 4: Prepare the Milk Mixture: In a large bowl, whisk together the evaporated milk, sweetened condensed milk, 1 cup heavy cream, and 1 teaspoon vanilla extract.
Step 5: Soak the Cake: Slowly pour the milk mixture evenly over the entire surface of the cake, ensuring it soaks into all the holes.
Step 6: Refrigerate the Cake: Cover the cake with plastic wrap and refrigerate for at least 3 hours, or preferably overnight, to allow the cake to fully absorb the milk mixture.
Step 7: Prepare the Whipped Topping: In a cold bowl, whip the cold heavy cream with an electric mixer until soft peaks form. Add the powdered sugar and teaspoon vanilla extract, and continue whipping until stiff peaks form.
Step 8: Frost the Cake: Spread the whipped topping evenly over the soaked cake. Dust with ground cinnamon, if desired.
Step 9: Serve: Cut the cake into squares and serve chilled.
Tip: For a richer flavor, add a tablespoon of rum or brandy to the milk mixture. Can also substitute almond milk for evaporated milk to cut down on sweetness.