My Mom’s Ah-Ma Sponge Cake Recipe (budgetpantry.com)
Makes one 6″ x 8.5″ cake

What you need:
60g butter
15ml oil (any oil like corn oil, olive oil)
90g plain flour, sifted
6 eggs (55g), whites and yolks separated
60ml milk
A small pinch of salt
15ml lemon juice
75g caster sugar

Steps:

Preheat oven to 160C and line your cake pan with baking paper.

Melt butter and oil over a bain marie. When melted, remove from stove top and add the flour. Stir with a whisk till combined.

Add the milk and egg yolks.

Continue to stir till mixture becomes creamy.

Now we beat the egg whites. Add the egg whites into your mixer and add a small pinch of salt. Start the motor on low and beat till you start to see froth. Add the lemon juice and 1/3 of the sugar and beat on high. As the egg white starts fluffing up, add the remaining sugar in two instalments and continue beating on high till it’s at a stage between soft peaks and stiff peaks (i.e., don’t over do it)

Add 1/5 of the egg white to the butter mixture and mix gently with a spatula. No need to fold at this stage.

Now the folding starts. Gently fold in the rest of the egg white in stages. Once you add the first scoop of egg white, start folding with your spatula from bottom up (never attack the egg white from the center or stir!). Repeat the folding until all the egg white is incorporated and mixture becomes thick and creamy.

Transfer mixture into cake pan and lightly drop the pan 1-2 times on the table before sending it to the oven.

Bake at 160C for 1 hour in a water bath. You can refer to this page if you’re unfamiliar with a water bath (no need to wrap with foil since we’re not using a springform pan). Once cake is done, remove from pan and cool before slicing.