In a large mixing bowl, combine the instant vanilla pudding mix with 2 cups of whole milk. Beat on medium speed for about 5 minutes until thick and creamy. Fold in 1/2 cup of lemon curd and set aside.

In a separate bowl, blend room-temperature mascarpone cheese with 2/3 cup of powdered sugar until smooth. Gradually add the juice of one lemon while mixing until stiff peaks form.

Carefully fold the pudding mixture into the mascarpone mixture until just blended.

Layer ladyfinger biscuits in a baking dish, briefly dip in a mixture of Limoncello and water, then spread half of the mascarpone mixture over them. Repeat with more ladyfingers and top with remaining cream.

Spread the rest of the lemon curd over the top of the tiramisu. Cover and refrigerate for at least 6 hours or overnight.

Once chilled, slice into squares and serve with optional whipped cream or lemon slices.