Beat the eggs with the sugar until light and fluffy. Gradually add the flour, gently folding it in from the bottom up until fully incorporated. Spread the batter onto a baking sheet lined with parchment paper and bake at 340°F (170°C) for 12 minutes. When done, sprinkle with a little granulated sugar and let cool.

Meanwhile, prepare the lemon cream. Combine all the ingredients in a small saucepan and cook over low heat, stirring constantly. When it starts to thicken, remove from heat and pour into a bowl. Cover with plastic wrap directly on the surface to prevent a skin from forming, and let cool.

For the mascarpone and lemon cream: In a saucepan, combine the water and lemon peels. Bring to a boil, then remove from heat and let infuse. Once cooled, strain and add the sugar. Cook until it reaches 250°F (121°C) (use a kitchen thermometer; this step is to pasteurize the yolks). Beat the egg yolks and slowly pour in the hot syrup while continuing to beat until completely cooled.

In a bowl, mix the mascarpone with the lemon cream, the lightly whipped cream, and the limoncello. Soak the gelatin sheets in cold water until soft, then squeeze out excess water and melt them in a small saucepan with 3 tablespoons (about 50 grams) of the cream taken from the total and already warmed. Add the melted gelatin to the cream mixture, then gently fold in the cooled yolks.

For the limoncello syrup: In a small saucepan, combine the water and sugar and heat until the sugar dissolves. Remove from heat, add the limoncello, and stir.

Cut the sponge cake base to fit a 9-inch (24 cm) pan. Place the cake in the pan and soak it with the warm syrup. Pour 2/3 of the lemon cream over the cake, smoothing it evenly. Place the remaining third of the cream in a piping bag (add yellow food coloring if desired). Use the piping bag to decorate the top as you like. Refrigerate for at least overnight before serving.