Preparation

• The eggs should be at room temperature. Remove them from the fridge the day before or a few hours in advance to let them acclimate.
• When there are 30 minutes left before baking, preheat the oven to 180 ºC, with heat from above and below.
• Line the mold if it's a detachable type, using baking paper or lightly greasing with butter and flour.
• First, whip the egg whites until stiff peaks form; when they start to foam, add the sugar and a pinch of salt. Whip them until you achieve a stiff peak (they shouldn't move if you tilt the bowl).
• Whiten the egg yolks with the sugar in a warm bain-marie until they double in volume. This usually takes about 10 to 15 minutes with electric beaters.
• Sift the potato starch over the bowl with the yolks. DO NOT Stir to avoid deflating them.
• Pour one-third of the whipped egg whites into the yolk bowl with the starch and gently stir with a manual spatula, using smooth motions from bottom to top to retain the air.
• Incorporate the rest of the whipped egg whites, stirring carefully to maintain the lightness.
• Fill the mold up to three-quarters of its capacity to allow room for expansion.
• Place the tray in the lower part of the oven (second guide counting from the bottom).
• Lower the oven temperature to 170 ºC and set it to operate with only the bottom heat.
• Bake at 170 ºC for about 30 minutes (Bottom Heat Only). Note: The baking time will vary depending on the size of the molds; if they are individual-sized, they might need only about 10 minutes.
• Turn off the oven and DO NOT Remove the cake or open the door. Wait 5 minutes to prevent it from losing volume.
• Slightly crack open the oven door and place a wooden spoon between the door and the oven to keep it ajar. Wait an additional 5 minutes.
• Open the door a little more and Wait another 5 minutes for continued gradual cooling.
• Finally, take the cake out of the oven and let it cool completely on a wire rack.
• Before serving, dust with powdered sugar on top. Note: The risk with sponge cakes is that when they are taken out of the oven, they tend to lose volume and appearance as they absorb moisture during the cooling process. This is what the staggered cooling attempt aims to prevent.