For the sponge cake
For the Roll
Line the baking tray with baking paper and heat to 180º with heat up and down. Separate the egg whites from the egg yolks and whip the egg whites until stiff with half of the sugar. Reserve. Whip the egg yolks with the rest of the sugar until they whiten and increase in volume. Combine both mixtures and add the sifted flour with wrapping movements so as not to lose the air.
Spread the mixture on the baking sheet to a thickness of less than 1 cm and bake for 10 minutes at 180º.
When removing from the oven and with the cake sheet still warm, place another piece of paper on top of the cake and flip it over to remove the paper used as a base. In this way we avoid that when it cools down it cannot be peeled off. Let stand.
Separate the whites from the yolks of the three eggs. Mix the egg yolks with the sugar until slightly whipped so that the sugar melts. Carefully add the mascarpone cheese, trying to keep it as low as possible. Whip the egg whites until stiff and add them to the above, trying to obtain a fluffy and not liquid mass.
If at this point we see that we have beaten the batter too much and it is more liquid than it should be, we can add one more beaten egg white. Care must be taken in this step as we will use this cream to fill the arm and otherwise it will all come out. We can also use a little neutral gelatin to stabilize the cream. Dissolve it in one or two tablespoons of warm milk and integrate it with the egg yolks and sugar.
Carefully roll out the sponge cake sheet and dip it, with the help of a brush, with the coffee and liqueur mixture. The point of wetting is to our taste, but be careful not to do it too much so that the iron does not break and expel liquid. Fill with the cream, leaving about three centimeters without covering the edge, and smooth with a trowel or knife.
Carefully roll up and place on the serving platter. Refrigerate for at least four hours, or better overnight covered with foil.
Just before serving, sprinkle with cocoa powder and garnish, if desired, with a few mint leaves.