How to make
Separate the egg whites from the yolks of the three eggs and beat them separately - the egg whites together with the fourth one into a thick mixture and the yolks along with the sugar into a light cream.
Add the oil, the salt, lemon juice and peel, rum and vanilla to this cream.
Beat again and add the starch (fine corn flour) in portions along with the baking powder.
Add the egg whites little by little to the resulting mixture, while stirring gently with a wooden spoon, so that they don't loose their volume.
Pour the mixture into a 8.7″ (22 cm) diameter cake tin, covered with baking paper and place it in a preheated oven at 360°F (180 degrees) for about 30 minutes or until it is fully baked.
When the cake is ready, turn off the oven and leave it inside for a few minutes, with the door left slightly ajar, then take it out and wait for it to cool.
Spread the foam cake with jam of your choice and squirt the whipped cream on top.
