This luscious cake is a spin on tres leches (three milks) cake, so named for the condensed milk, regular milk, and coconut milk (used here) that's poured over the cake after baking and infused it with incredible flavor. You need a light cake to soak up that much liquid, and that's why this cake recipe calls for beaten egg whites to be folded into the batter, and which needs no other fat except for that provided by the yolks.