Prepare the cake: Preheat oven to 350 F. Grease a 9 x 13 inch pan.
Combine flour, baking powder, and salt in a large bowl.
Separate eggs. Beat the yolks, gradually adding 3/4 C sugar until pale and frothy. Stir in milk and vanilla. and gently combine with flour mixture.
Beat whites until soft peaks, then slowly add the remaining 1/4 C sugar until stiff peaks (French meringue, do not over beat!)
Fold the whites gently into the rest of the batter.
Pour into prepared pan and tap to even the surface. Bake ~30 min until set.
Whisk together all of the above ingredients for the leche.
Pierce the surface of the cooled cake with a fork and pour the leche over the cake, allowing it to absorb the liquid. You may have to wait up to 30 min for the cake to take all of the liquid. If it sits overnight in the fridge, even better!
Although the whipped cream topping is tasty, I encourage you to try a meringue at least once for both texture and aesthetic. I recommend using an Italian meringue here since the stability is helpful in serving the cake.
Boil the water and sugar together until it reaches soft ball stage, 235-240 F.
Meanwhile, beat the egg whites to soft peaks, add vanilla/rum.
Slowly pour the hot syrup into the egg whites, beating constantly.
Beat until the bowl is cool and the meringue is glossy. Spread or pipe in a design onto the cool cake. I like to run a torch over the meringue for a few seconds to give it nice golden peaks.
Decorate with slices of mango, or as in our case, flambéed bananas.