Zest one lemon with a microplane, then juice it and measure out 2-3 tablespoons; set both the zest and juice aside.

Beat 16 oz of mascarpone cheese in a large mixing bowl until smooth, then gradually add 8 oz of heavy whipping cream and mix until fluffy.

Gently fold in the reserved lemon zest, lemon juice, and 1¼ cups of powdered sugar into the mascarpone mixture.

Soak half of the 7 oz package of ladyfinger cookies in 6 tablespoons of Limoncello briefly, then arrange them in a single layer in a 9x9 casserole dish.

Spread half of the mascarpone mixture over the ladyfingers to form the first layer.

Spoon 8 oz of lemon curd evenly over the mascarpone layer.

Repeat the layering process with the remaining ladyfingers and finish with the last layer of mascarpone mixture.

Cover the casserole dish with plastic wrap and refrigerate for at least 10 hours.

Before serving, sprinkle powdered sugar on top and garnish with lemon slices.