Preheat oven to 350°F (175°C). Grease and lightly flour a 9x13-inch baking pan.
In a medium bowl, whisk together flour and baking powder. Set aside.
In a large mixing bowl, beat butter and sugar with an electric mixer until light and fluffy.
Add eggs one at a time, beating well after each addition. Mix in vanilla extract.
Gradually add the flour mixture, mixing until just combined.
Pour batter into the prepared pan and spread evenly.
Bake for 30 minutes, or until a toothpick inserted in the center comes out clean.
Let the cake cool completely, then pierce the surface all over with a fork.
In a medium bowl, whisk together whole milk, sweetened condensed milk, and evaporated milk.
Slowly pour the milk mixture evenly over the cake, allowing it to soak in.
Refrigerate for at least 1 hour to let the cake absorb the milk.
In a chilled mixing bowl, whip heavy cream, sugar, and vanilla until soft peaks form.
Spread whipped cream evenly over the cake.
Keep refrigerated until ready to serve.