Preheat your oven to 160°C.

Place the white sugar into a saucepan or small pot.

Cook over low heat while stirring continuously until the sugar completely melts and turns into a beautiful golden caramel.

Immediately pour the caramel into your cake pan and swirl the pan so the bottom is evenly coated.

Set aside.

In a bowl, combine: evaporated milk, egg yolks, condensed milk, and vanilla extract.

Mix gently until smooth without incorporating too much air.

Strain the mixture into another bowl to remove any egg solids.

Pour the smooth custard over the caramel inside the cake pan.

Set aside.

In a large bowl, sift together: cake flour and all-purpose flour.

Add: sugar, baking powder, salt. Mix well.

Add: cooking oil, evaporated milk, egg yolks, and calamansi juice. Mix until the batter becomes thick but still flows smoothly. Do not overmix.

Using a clean, dry mixing bowl, add the egg whites and cream of tartar.

Beat until bubbly.

Gradually add the sugar while continuously beating.

Continue beating on high speed until stiff peaks form.

Add one-third of the meringue into the batter.

Fold gently using the cut-and-fold method.

Repeat with the remaining meringue in two batches.

Continue folding just until no white streaks remain. Avoid overmixing because this deflates the batter.

Carefully pour the chiffon batter over the leche flan mixture. Do not stir.

The cake batter will naturally float on top during baking while the flan settles beautifully.

Place the cake pan inside a larger baking tray.

Pour hot water into the tray to create a water bath.

Bake at 160°C for approximately 35 minutes or until a toothpick inserted into the cake comes out with no wet mixture.

Allow the cake to cool completely.

Run a thin knife around the edges if needed.

Place a serving plate over the pan and carefully invert the cake.

Refrigerate before serving.

Enjoy your delicious homemade Custard Cake!