Make the Cake Batter:

1. Preheat the oven to 350ºF (175ºC). Grease and flour a 9×13-inch cake pan.
2. Separate the eggs gently cracking the egg and transfer the yolk back and forth between the shell halves until the white separates into a bowl.
3. In the bowl of a stand mixer fitted with the paddle attachment, beat the egg yolks, vanilla extract and granulated sugar until smooth and double in volume. 
4. Fold in the flour, salt and baking powder into the egg yolk mixture. Do not over mix. 
5. In a clean, dry bowl, whisk the egg whites on high speed, until stiff peaks form and the mixture is glossy. About 6-8 minutes.
6. Fold the whipped egg whites into the cake batter until no streaks remain.
7. Pour the batter into the prepared cake pan and spread it evenly. Bake for 15-18 minutes, or until a toothpick inserted into the center comes out clean and the top is golden brown. 
8. Once cooled, use a skewer or fork to poke holes all over the top of the cake.

Make the Milk Mixture:

1. In a large bowl or jar, combine the evaporated, condensed and whole milks. Refrigerate until ready to use.

Soak the Cake:

1. Pour the milk mixture, one cup at a time, until it begins to soak. Refrigerate, covered with foil, for at least 4 hours, but preferably overnight.

Make the Meringue Topping:

1. In a bowl, combine the egg whites, sugar and cream of tartar until well mixed. Place the bowl over a small saucepan with simmering water and cook, stirring constantly, until the sugar dissolves and reaches 160ºF.
2. Beat the eggs whites with a hand mixer or stand mixer fitted with the whisk attachment, until stiff peaks form and meringue becomes glossy.
3. Spread the meringue evenly over the soaked Tres Leches Cake.
4. Use a kitchen torch to lightly brown the meringue.
5. Slice and serve.