Preheat your oven to 160°C.

In a large bowl, combine the cake flour, all-purpose flour, baking powder, salt, and sugar. Mix until well combined.

Add the evaporated milk, egg yolks, and cooking oil. Stir until smooth.

Pour in the calamansi juice or lemon juice. Mix until the batter becomes thick but still flowy or slightly runny.

In another clean mixing bowl, add the egg whites and cream of tartar.

Beat until bubbly.

Gradually add the sugar while mixing.

Continue beating on medium-high speed until stiff peaks form.

Add one-third of the meringue into the batter and gently fold to lighten it.

Add the remaining meringue in two more batches.

Fold carefully using the cut-and-fold method until the batter becomes uniform in color. Avoid overmixing.

Prepare your baking pan by lining it with parchment paper or lightly greasing it with oil if preferred.

Pour the batter into the prepared pan.

Bake at 160°C for 25 to 30 minutes, or until a toothpick inserted into the center comes out with no wet batter.

After baking, you may notice slight cracks on top. This is completely normal and they will settle as the cake cools.

Immediately invert the pan onto a cooling rack to prevent excessive shrinking.

Allow the cake to cool completely before removing it from the pan.

Serve at room temperature or chill in the refrigerator before serving for an even more refreshing treat.