Preheat the oven to 170C (338F), then line the baking tray (12 x 10 inch) with silicone paper. Sift plain flour.
Have a skillet with hot water ready (or a bain marie).
In the glass bowl with eggs and sugar placed on bain marie, use a hand whisk to beat the mixture until all dissolved and the temperature reach 40C (104F).
Remove the glass bowl (place a bowl of milk to the bain marie to warm it up for later use).
Using a hand mixer/stand mixer with a paddle or a whisk attachment to beat the egg and sugar mixture, start from high speed, beat until the mixture raise 3 times.
Then first add half of sifted flour then practice the Fold-in method, fold from the bottom to the top by rubber spatula, then add the remaining of sifted flour then repeat the process.
Add warm milk to the mixture, then slowly stirring by a hand mixer till all combined, don't over mix it.
Pour the batter over the lined baking tray, level and smooth the surface by a plastic scrapper.
Bake at 170C (338F) for around 10 minutes till the sponge is cooked.
Remove cake from the oven and allow to cool. Cake will be a little bit yellow and looks very leveled (easy to assemble)