Prepare steamer by boiling 2 liters of water.
Set molds on the stove under low-heat setting. Add sugar and gently swirl using until it caramelizes. Set aside to cool and harden on a flat surface.
Whisk yolks in a bowl. Add condensed milk and vanilla extract. Mix thoroughly.
Pour mixture into molds. Cover with foil.
Steam for 30 mins on low heat stove setting.
Using a knife, thin spatula, trace lining of molds to loosen the flan. Put serving plate on top and turn upside down. Tapping the bottom of the mold helps to transfer flan to the plate.
Set aside to cool then serve. (Best served cool.)
