Coat bahulu mould with oil, wipe out excess oil with kitchen towels. Preheat the mould in oven to 210°C/410°F. (Reminder: Coat only once with oil. )
Beat eggs lightly, add in salt and sugar, beat until combined.
Combine 1 Liter of plain water with 400 ml of hot water (from electric thermo pot) in a large steel bowl to yield warm water with temperature about 45°C/113°F.
Dip mixing bowl in warm water bath, beat egg mixture over medium-high speed until stiff (about 5 minutes). (Reminder: Beating egg mixture over warm water will shorten the time for it to become stiff.)
Combine plain flour and cornstarch, sift twice.
Sift flour into egg mixture in 3 batches, fold gently until well mixed with spatula. Add in melted butter gradually, fold gently until well mixed. (Reminder: Since the batter needs to be baked in 5 batches, it is important to prevent egg mixture from deflating, folding flour into egg mixture with spatula is better than using mixer.)
Pour batter into piping bags.
Take out the preheated bahulu mould, continue to preheat oven to 210°C/410°F. Fill batter into the hot mould.
Bake in the preheated oven at 210°C/410°F for 8.5 to 9 minutes, until golden brown.
Clip the cut part of piping bag, push the remaining batter down together, then clip the piping bag and wait for the next batch. (Reminder: This will help preventing batter from deflating fast.)
Remove the baked bahulu, continue to preheat oven to 210°C/410°F for the next batch.
Unmould and cool bahulu on wire rack.
Fill batter again into hot mould, prepare to bake the next batch. Repeat the steps, until all batter is used up.
This recipe yields 60 pieces of kuih bahulu. The nutritional value for reference is for 1 piece.