Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking dish with butter, dusting it lightly with flour.

In a medium bowl, whisk together the flour, baking powder, and salt until well combined.

In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy.

Add the eggs one at a time, mixing well after each addition, followed by the vanilla extract.

Gradually add the dry ingredients to the butter mixture, alternating with the whole milk, and mix until just combined.

Pour the batter into the prepared baking dish and bake for 25-30 minutes until a toothpick comes out clean.

Allow the cake to cool in the pan for about 30 minutes before transferring to a wire rack.

While it cools, whisk together the sweetened condensed milk, evaporated milk, and heavy cream.

Once the cake is cool, poke holes all over the surface and pour the soaking mixture evenly over it.

Refrigerate the cake for at least 2 hours, preferably overnight, to allow flavors to meld.

Before serving, top the cake with diced mango and garnish with mint leaves if desired.