To prepare the layer, first beat the egg yolks with half of the powdered sugar. Separately, beat the egg whites with a pinch of salt to hard snow and then mix them with the remaining powdered sugar. They need to become very hard.
Gently mix the egg whites in to the yolks. Sift the flour with the starch and mix them with the egg mixture.
Finally mix in the cocoa. Pour the mixture into a baking dish, covered with baking paper and put the cake layer to bake for 15 minutes in a preheated 392°F (200 °C) oven. Once baked, allow it to cool slightly and take it out onto a cooking grid. Once completely cool, mix it with a mixture of the liqueur and strong espresso.
To prepare the cream, soak gelatin in cold water ahead of time to soften. In a water bath (not boiling water), beat the egg yolks, powdered sugar for the cream and vanilla together, until they turn to foam.
Squeeze the softened gelatin and add it to the slightly warmed rum and lemon juice. Pour the egg mixture into the gelatin and mix well. Allow the cream to cool. Then stir and mix well with the mascarpone.
Separately, beat the liquid cream with the vanilla sugar and add it to the egg mixture that's already started to gel. With this cream, cover the cake layer thoroughly and smooth it out. Leave in the fridge for 4-5 hours.
Before serving, cut the tiramisu into square pieces. Serve sprinkled with plenty of cocoa.