Heat water and 1/4 cup sugar in small pot over medium heat until sugar is dissolved.
Remove from heat.
Add lemon juice & 1/4 cup limoncello.
In a small bowl add ¼ cup sugar to defrosted raspberries. Stir.
Combine mascarpone, ½ Tb. lemon zest, ¼ cup limoncello, and ½ cup sugar in stand mixer. Whisk on medium speed 1 minute.
Add ½ cup whipping cream, mixing slowly. When combined, turn to high and beat for 30 seconds.
Place ladyfingers in a single layer on a rimmed baking sheet.
Spoon lemon simple syrup over 30 ladyfingers. (You may have a small amount leftover.)
Sprinkle powdered sugar on bottom of 8×8 pan.
Line bottom of pan with ladyfingers (about 15).
Spread half of raspberry mixture over ladyfingers.
Spread half of mascarpone mixture over raspberries.
Repeat with powdered sugar, ladyfingers, raspberries, and mascarpone.
Cover; refrigerate overnight.