Bibingkang Cassava (Cassava Cake)

Preheat the oven to 350°F.
To make the cake, combine the egg yolks, cassava, macapuno (or shredded coconut, if using), coconut milk and the ½ cup sweetened condensed milk in a large bowl and mix well.
Pour the cake batter into a greased 8 x 8-in (20 x 20-cm) cake pan. The cake batter will appear to be very loose and wet at this point, but don’t worry, the cassava will absorb most of the liquid during baking. Place the cake pan into the oven and bake until the top of the cake appears dry and no liquid is floating on the surface, 45–60 minutes.
Meanwhile, to make the topping, whisk together the egg whites and the ¼ cup (65 ml) sweetened condensed milk in a medium bowl until very well incorporated. Although you are using egg whites, don’t be concerned with making a foam or a meringue, just mix until combined.
Remove the cake from the oven and evenly pour the topping onto the cake. Return the cake to the oven and bake until the topping sets, about 10 minutes more.
Remove the cake from the oven and rest the cake in its pan on a cooling rack. Cool the cake completely before cutting it into squares. The cassava cake can be served at room temperature, or cold out of the refrigerator.