Combine ½ cup water, ½ cup lemon juice, and ¼ cup sugar in a saucepan. Heat over medium, stirring until sugar dissolves. Remove from heat and cool. For an adult twist, add 1-2 tbsp limoncello once cooled.
Whip 1 cup heavy cream in a cold bowl until soft peaks form. Set aside.
Mix 1 cup mascarpone, ⅓ cup powdered sugar, 1 tsp vanilla extract, and 2 tsp lemon zest until smooth. Fold in whipped cream gently.
Dip each ladyfinger into the cooled lemon syrup for 1-2 seconds—don’t soak too long.
Layer soaked ladyfingers in an 8×8-inch dish. Spread half the mascarpone mixture on top. Add a thin layer of lemon curd if desired. Repeat with another layer of ladyfingers and mascarpone.
Cover and refrigerate for at least 4 hours, preferably overnight. Garnish with lemon zest, powdered sugar, or lemon slices. Slice and serve chilled.