Star by Preheating your oven to 325 degrees F. Lightly grease a 9 X 13 baking dish and set aside.
In a medium bowl, whisk together the flour, baking powder and salt; set aside.
Using an electric or hand mixer, beat the butter, sugar and vanilla extract until very pale and creamy. Periodically scrape down the sides of the bowl.
Add the eggs, one at a time, beating well after each addition. Reduce the mixer speed to low and gradually add the flour mixture, mixing until just combined.
Scrap the bowl again and stir the batter to ensure all of the ingredients are well mixed.
Transfer the cake batter to the prepared baking dish. Bake until a toothpick inserted into the center comes out clean, 40 to 50 minutes. Allow the cake to cool completely in the pan.
In a large mixing cup or medium bowl, whisk together the whole milk, sweetened condensed milk, buttermilk, dulce de leche, and vanilla extract until combined.
Using a a knife or the back side of a mixing spoon, poke holes all over the top of the cake.
Very slowly, pour the milk mixture all over the cake. Cover and refrigerate the cake for at least 3 hours, or overnight, ensuring that all of the milk mixture is absorbed.
Place the cream in a large bowl along with 1 Tablespoon of dulce de leche and whip with hand or stand mixture until peaks form.
Spread the whipped cream on top of the cake, then drizzle lines of dulce de leche over the cake. Drag a butter knife or toothpick over likes to create decorative swirl topping.
