In a clean dry bowl, beat the egg whites until soft peaks form. Add in the sugar little by little, beating after each addition.
Continue beating until the mixture is firmer and fluffier (about 5 min).
Incorporate the flour and the baking powder with a rubber spatula, making outside in movements.
Pour this mixture in a rectangular pan with high walls and bake at 350°F for 30 min. or until a wooden stick comes out clean when inserted.
Pour the batter into a rectangular pan and bake for about 30 min. or until golden brown.
Let the cake cool completely.
For the tres leches mixture:
In a large bowl whisk together the sweetened condensed milk, evaporated milk, sweet cream, vanilla extract salt and ron.
Mix with a wooden spoon until it is all well incorporated and set aside.
For the meringue:
In a small saucepan, combine sugar and water. Heat over high heat, brushing down sides of pot as necessary with a pastry brush dipped in water. Cook until sugar syrup registers 240°F on an instant read or candy thermometer (this can also be tested dripping some syrup in cold water; if a soft ball forms, it´s ready!). ake away from the heat when ready.
Meanwhile, combine egg whites with cream of tartar and lemon juice in the bowl of a stand mixer. Set mixer to medium speed and mix until soft peaks form, about 2 minutes.
With the mixer running, carefully and slowly drizzle in hot sugar syrup. Increase speed to high and whip until desired stiffness is achieved.
To assemble:
Pierce the cake all over the top with a fork and set aside.
Pour the tres leches mixture slowly all over the top of the cake so that it all soaks in the tender sponge.
Refrigerate the cake for 30 min. or until all the juices absorb.
Spread the meringue all over the top of the cake and decorate to your liking.