Preheat the 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 mixing bowl, cream the softened butter and 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 wet mixture, alternating with the whole milk. Mix until just combined and smooth.

Pour the batter into the prepared baking dish and bake for 25-30 minutes, or until a toothpick inserted in the center comes out clean. Let the cake cool completely in the pan.

In a separate bowl, combine the sweetened condensed milk, evaporated milk, and heavy cream. Once the cake is cool, poke holes all over the top with a fork or skewer.

Slowly pour the milk mixture over the cake, allowing it to soak in. Cover the cake and refrigerate for at least 2 hours, or overnight for best results.

Before serving, top the cake with diced mango and whipped cream if desired. Garnish with fresh mint leaves.