Prepare the syrup: In a deep plate, add the hot water and sugar and mix until the sugar dissolves. Add the limoncello and lemon juice and set aside.

Prepare the tiramisu cream: All ingredients should be cold.

Separate the egg whites from the yolks into two separate bowls.

Using a mixer, beat the egg yolks with half of the sugar until pale and creamy.

In the other bowl, whisk the egg whites with the rest of the sugar, gradually increasing the mixer speed, until stiff peaks form.

Lowering the mixer speed or using a spatula, add the mascarpone one spoonful at a time, seamlessly integrating it with the limoncello, lemon juice, grated zest and the whisked egg yolks. Then gently fold in the whipped egg whites at the end to keep the cream light and airy.

Assemble the tiramisu: Soak 1/3 of the ladyfingers, one at a time, in the limoncello syrup and arrange them in a single layer on the bottom of the serving tray.

Cover the first layer of ladyfingers with 1/3 of the cream and continue assembling until the last layer. Refrigerate the assembled tiramisu for 4 hours or overnight before serving.

Meanwhile, prepare the caramelized lemons: In a pan over medium heat, add the water and sugar and mix until dissolved.

Keep stirring until you get a thick, caramel-like syrup. Add the lemon slices in a single layer and let them cook for 7-10 minutes.

Turn the slices over and continue cooking. Transfer the caramelized slices to a baking sheet to cool for a few hours or overnight.

Garnish the tiramisu with the caramelized lemon slices and serve.