First, start by adding the flour, baking powder and salt to a bowl. Whisk together to combine and set aside for now.
Separate the eggs from the yolks very carefully. Make sure the whites are inside of a clean bowl and that you don’t mix any yolk in with the whites.
In a stand mixer, combine the butter and sugar. Mix until you have a creamy consistency. This may take about 3-5 minutes.
Add the egg yolks one at a time while continuing to mix.
Mix in the vanilla extract and 1/2 cup of milk.
Preheat the oven to 350 degrees F.
Begin adding the flour mixture about 1/4 cup at a time to the wet ingredients while mixing. Stop to scrape the sides of the bowl as needed.
Transfer the cake batter to a separate bowl and thoroughly wash and dry the mixer and mixing bowl.
Add the egg whites to the clean mixing bowl and mix on high speed until stiff peaks form.
Pour the beaten egg whites into the cake batter prepared earlier. Fold the egg whites in using a spatula just until it is incorporated into the batter.
Pour the cake batter into the baking dish and bake at 350 degrees F for 25-30 minutes or until a toothpick inserted in the center comes out dry.
Remove the cake from the oven and use a fork to poke holes into it. Don’t poke all the way to the bottom because you want the Tres Leches glaze to sit inside the cake and not escape from the bottom.
In a bowl, mix together the sweetened condensed milk, evaporated milk and whole milk. Pour this glaze over the cake about 1/2 cup at a time. Do this about 2-3 times or as many times as you wish depending on how moist you want the cake.
Top with whipped cream and guava marmalade dollops. Swirl the guava marmalade into the whipped cream topping to form nice patterns.
Refrigerate for at least 4 hours or overnight, serve and enjoy!