Preheat your oven to 350°F (175°C). Grease and flour a 9x13 inch baking dish.
In a medium bowl, whisk together the flour, baking powder, and salt. Set aside.
In a large bowl, cream the softened butter and granulated sugar together until light and fluffy.
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
Gradually add the dry ingredients to the butter mixture, alternating with the whole milk. Mix until just combined.
Pour the batter into the prepared baking dish and smooth the top. Bake for 30-35 minutes, or until a toothpick inserted in the center comes out clean.
While the cake is baking, prepare the milk mixture. In a bowl, combine the sweetened condensed milk, evaporated milk, and heavy cream. Whisk until well blended.
Once the cake is done, remove it from the oven and let it cool for about 10 minutes. Poke holes all over the top of the cake with a fork.
Slowly pour the milk mixture over the warm cake, allowing it to soak in. Let the cake cool completely, then refrigerate for at least 2 hours or overnight for best results.
Before serving, whip the heavy cream with powdered sugar and vanilla extract until soft peaks form. Spread the whipped cream over the top of the cake.
Garnish with fresh fruit or a sprinkle of cinnamon if desired. Cut into squares and serve chilled.