Preheat Oven: Preheat your oven to 350°F (175°C). Grease a 9×13-inch baking dish.
Make the Cake Batter: In a large mixing bowl, cream the butter and sugar together until smooth. Add the eggs and vanilla, beating until light and fluffy.
Combine Dry Ingredients: In a separate bowl, sift together the flour, baking powder, and salt.
Mix Wet and Dry Ingredients: Gradually mix the dry ingredients into the wet ingredients until well combined.
Bake the Cake: Pour the batter into the prepared baking dish and bake for 30-35 minutes, or until a toothpick comes out clean. Let it cool.
Cool and Pierce the Cake: Pierce the cooled cake all over with a fork.
Make the Milk Mixture: In a bowl, whisk together the whole milk, evaporated milk, and sweetened condensed milk.
Soak the Cake: Pour the milk mixture over the cake and allow it to absorb for 30 minutes.
Make the Whipped Topping: Whip the heavy cream, sugar, and vanilla extract until stiff peaks form.
Top the Cake: Spread the whipped cream over the cake and sprinkle with cinnamon if desired. Refrigerate and serve chilled.