Prep: Grease a 13x9 pyrex pan or smaller and preheat oven to 325 degrees. Mix flour and baking powder and sift several times.
Sponge Cake: Beat the eggs and salt in a mixer (without separating the whites from yolks). When the eggs are foamy, starting adding the sugar gradually and beat well until mixture changes color (turning light lemony color).
Stop mixer and pour in the 1/4 c milk, mixed with the vanilla, all at once. Then add flour, 1/3 at a time. Mix the last third of flour by hand, folding it gently so as not to deflate the egg/flour mixture. Place in prepared pan and bake for 25 minutes or until lightly browned on top.
While the cake is cooking, mix the three milks* (condensed, evaporated, whipping cream) in a pan and bring to a soft boil to reduce so it won't be so runny when you pour it over the sponge cake. Let mixture cool, don't pour it when it's still very hot. Rum extract may be added to milk mixture if desired.
When cake is done and has rested a few minutes, poke holes with a toothpick and gently pour the milk mixture, waiting for the milk to be absorbed by the cake before you pour some more. You may tip the pan to the sides so the milk is evenly distributed throughout the cake. Let it rest to cool enough so the vapor will not condense when you cover with plastic wrap. Let it cool completely in the refrigerator for a few hours before serving or overnight.
Add cool whip on top when ready to serve. You may sprinkle the top with toasted slivered almonds or toasted coconut.