Prepare a baking pan larger than 8 inch. Fill with water then put inside the oven. Preheat the oven 340°F.

Line an 8 inch round pan with parchment paper. Put aside.

Mix the egg yolks, whole egg, salt and vanilla extract with hand whisker. Set aside.

Heat the butter over low heat until small bubbles start to appear at the bottom of the melted butter.

Pour the flour into the hot melted butter. Fold to mix with a spatula. Add in the condensed milk. Stir to combine. Turn the heat off.

Pour the flour mixture to the egg yolk mixture. Stir until well combine and smooth.

Beat on low speed the egg whites until foamy with an electric mixer. Add in the sugar in 3 batches. Beat on medium or medium high until stiff peaks form.

With a spatula, fold in the meringue into the egg yolk mixture in 3-4 batches.

Pour the batter into the prepared cake pan. Lightly bang the pan a few times to remove any trapped air bubbles in the batter.

Carefully put the pan inside the other pan which filled with water (from the oven). Put them all back to the oven. Bake for 40 minutes. Turn the oven temperature down to 320°F and bake for 25 minutes. Test with skewer to see if it's done. The skewer should come out clean.

Once cooked, remove it from the oven, leave it for 15-20 minutes then take the cake out from the pan. Leave it on the wire rack until it gets cool.