Preheat the oven to 350ºF.
Using a mixer, cream butter and sugar together until pale, light, and fluffy (about 3 minutes). Scrape the sides of the bowl as necessary. Add in the eggs one at a time, beating well after each one. Add in the vanilla and mix just until incorporated.
Sift together the flour, baking powder, and salt. Add the flour mixture into the batter one scoop at a time, mixing well after each addition. Mix until there are no more streaks of flour.
Butter a glass or other oven-safe baking dish. Pour the cake batter into the pan and spread the batter into an even layer.
Bake for 30-35 minutes, until a cake tester comes out clean.
Pour all of the condensed milk into a bowl and add in the evaporated milk in three parts. Mix well after each addition. Add the whole milk in last and mix until the mixture is of uniform consistency. Cover and place in the refrigerator.
When the cake is finished baking, place on a cooling rack. Use a toothpick or skewer to poke holes all throughout the cake. Let the cake cool completely (about two hours).
Once the cake has cooled, pour half of the milk mixture over the cake and let it absorb. Then, pour in the second half of the mixture.
Cover cake and refrigerate for at least 30 minutes or ideally overnight.
When ready to serve, whisk the heavy cream until thickened into whipped cream. Spread a layer over the cake. Serve and enjoy!
