In a mixing bowl, combine the mascarpone, powdered sugar, and 2 tablespoons (about 30 grams) of brown sugar. Beat with an electric mixer until creamy. Gradually add the cold heavy cream, mixing until fully incorporated and smooth.

Add the zest and juice of one lemon and 2 teaspoons (about 10 ml) of limoncello. Mix until the cream is smooth and homogeneous, then refrigerate.

For the syrup: In a small saucepan, combine the water (1 2/3 cups/400 ml), remaining brown sugar, and the zest of one lemon (avoid the white pith). Stir and bring to a boil. Remove from heat and let cool. Transfer to a bowl, add 4 teaspoons (about 20 ml) of limoncello, mix well, and set aside. Take the cream out of the fridge and start assembling the tiramisu.

Spread a layer of lemon cream on the bottom of a baking dish. Dip the pavesini cookies in the limoncello syrup and arrange them over the cream. Cover with another layer of lemon cream, add another layer of soaked pavesini, and finish with the remaining lemon cream.

Sprinkle with chopped pistachios. To caramelize lemon slices: In a nonstick pan, add 4-5 tablespoons granulated sugar and 1 tablespoon limoncello. Bring to a boil, add thinly sliced lemon, and caramelize, making sure they don't get too dark. Once caramelized, place on parchment paper and let cool.