Grate the lemon zest and leave to infuse for about 20 minutes in lemon juice.
In a pot, whisk the egg yolks with sugar.
Strain the juice from the lemon zest and add it to the egg yolks, place the pot on the stove and cook the custard for 5 minutes. Turn off the heat and add butter.
Stir with a wooden spoon until the butter has completely melted and then cover the lemon cream with plastic wrap and store in refrigerator.
Meanwhile, prepare the Limoncello syrup: boil water with sugar and lemon zest for 1 minute.
Let it cool down and then add the Limoncello.
In a bowl, add the previously prepared lemon cream to the mascarpone cheese with a wooden spoon and with gentle movements. Add the cream which has been previously whipped. Mix all ingredients stirring gently with a wooden spoon. Assemble now the Lemon flavored Tiramisu. Slightly dip “Gastone Lago ” lady fingers in the Limoncello syrup and place them on the bottom of a baking dish, creating the base of the tiramisu (if you prefer you can use glasses). Spread half of the mascarpone lemon cream over the lady fingers.
Cover with a second layer of slightly dipped “Gastone Lago” lady fingers. Top with the remaining mascarpone cream. Pour the remaining cream into a piping bag and decorate the tiramisu. Chill for about 3 hours.