Preheat the oven to 350 degrees F., grease a 9-inch square baking pan, and set aside.
In a small bowl, sift together the flour and baking powder and set aside.
In a large bowl, using a mixer on medium speed mix together the 3 large egg whites with the cream of tartar until soft peaks form. Slowly add in the sugar a tablespoon at a time until fully combined.
Mix in the egg yolks one at a time until combined. Turn the mixer on low and gradually add in the flour mixture stopping at least once to scrape the sides of the bowl, continue blending until the ingredients are combined.
Add in the milk and mix just until the ingredients come together. Pour the cake batter into the prepared pan and bake for 20 to 30 minutes until the center is set and a cake tester comes out clean.
Once you remove from the oven, allow the cake to cool in the pan on a cooling rack. Mix the heavy cream, evaporated milk, and condensed milk, until smooth. Use a toothpick to poke holes all over the top of the cake.
Slowly pour the milk mixture into the holes. Place the cake in the refrigerator for at least 1 hour or up to overnight. Top with whipped topping and toasted coconut prior to serving and store in the refrigerator.