Prepare the sponge cake without the butter. Then bake [Cook-timer minutes = "15"]15 minutes[/cooked-timer] at 100 ° C to dry (which will allow the cake to better absorb the coffee)
In a bowl, beat the egg whites until a frothy mixture is obtained then add half of the stevia and continue beating until the mixture becomes a shiny meringue.
In a second bowl, whisk together the egg yolks, salt and remaining stevia until a creamy, pale yellow mixture is obtained.
Add the mascarpone to the egg yolk mixture and mix well and add vanilla and half of the rum.
Once the mixture is homogeneous, gently stir in the meringue.
In a bowl, mix remaining rum with espresso. Wet the pieces of cake halfway up and place them in the bottom of the dish.
Cover with a layer of cream.
Repeat until filling the dish. Make sure that the last layer is the mascarpone cream.
Cover with a film and place in the fridge for at least 4 hours.
Once out of the fridge, sprinkle with cocoa and enjoy.