Step 1

The lemon curd was developed for this recipe; do not substitute another lemon curd. Do not allow the mascarpone to warm to room temperature before using; it has a tendency to break if allowed to do so. Be certain to use hard, not soft, ladyfingers.

Step 2

Whisk ⅔ cup sugar, eggs and yolks, and pinch salt in medium bowl until smooth. Heat ½ cup lemon juice in small saucepan over medium heat until hot and just bubbling around edges, 1 to 2 minutes. Whisking constantly, slowly pour hot lemon juice into sugar mixture and whisk until smooth. Transfer mixture to now-empty saucepan and cook over medium heat, stirring constantly with wooden spoon or silicone spatula, until mixture is thick enough to cling to spoon and registers 170 degrees, about 3 minutes.

Step 3

Immediately remove pan from heat and pour curd through fine-mesh strainer into small bowl (you should have 1 cup). Press lightly greased parchment paper directly on surface of curd and refrigerate until cool, at least 30 minutes or up to 24 hours.

Step 4

Using stand mixer fitted with whisk attachment, whip mascarpone on medium speed until no lumps remain, 1 to 11/2 minutes, scraping down bowl once or twice. Add remaining 1/8 teaspoon salt and ¾ cup lemon curd and continue to whip until just combined and no visible streaks of curd remain, about 1 minute longer. Transfer to large bowl and set aside.

Step 5

In now-empty mixer bowl, whip cream on medium speed until frothy, 1 to 1½ minutes. Add remaining 1 tablespoon sugar; increase speed to high; and continue to whip until cream holds stiff peaks, 1 to 1½ minutes longer. Fold one-third of whipped cream into mascarpone mixture to lighten, then gently fold in remaining whipped cream until no white streaks remain. Set mascarpone mixture aside.

Step 6

Combine limoncello, water, and remaining ⅓ cup lemon juice in wide bowl or baking dish. Place half of ladyfingers on counter. Drop 1 ladyfinger into limoncello mixture, roll (do not submerge; rolling should take 2 to 3 seconds for each cookie), remove, and shake off excess liquid. Place soaked cookie in 8-inch square glass or ceramic baking dish. Continue rolling and shaking ladyfingers and arranging them in single layer, breaking or trimming as needed to fit neatly into dish.

Step 7

Spread half of mascarpone mixture over ladyfingers; use offset spatula to spread mixture to sides and into corners of dish and smooth surface.

Step 8

Repeat dipping and arranging remaining ladyfingers; spread remaining mascarpone mixture over ladyfingers. Wipe edges of dish with dry paper towel. Dollop remaining ¼ cup lemon curd evenly on top of mascarpone in 9 places. Using small spatula or back of spoon, smear curd to create marbled design. Cover and refrigerate for 6 to 24 hours. Cut into pieces and serve chilled.