Make the lemon curd

• Combine eggs, sugar, lemon juice, and zest in a heavy-bottomed saucepan over medium-low heat.
• Whisk constantly for 5–7 minutes until the mixture reaches 180°F (82°C) or is thick enough to coat the back of a spoon.
• Remove from heat and immediately whisk in the cold, cubed butter until glossy and smooth.
• Transfer to a glass bowl, press plastic wrap directly onto the surface to prevent a skin, and refrigerate until completely cold (at least 2 hours).

Make the lemon syrup

• In a small saucepan, combine the water, sugar, lemon juice, and lemon zest. Place over medium heat and stir until the sugar is completely dissolved. Remove from the heat and let it cool.
• If you are using limoncello, stir it in once the syrup is cool.

Prepare the Mascarpone Cream

• In a large bowl, whisk the room-temperature mascarpone cheese, granulated sugar, lemon juice, lemon zest, and vanilla extract until smooth.
• Pour the cold heavy cream into the same bowl. Start your mixer on low to combine, then increase to medium-high.
• Once the cream reaches soft peaks, add the lemon curd and continue to whip until the mixture reaches stiff peaks.
• Note: Be careful not to over-whip; the mascarpone will firm up quickly once the cream is added.

Assemble and Top

• Briefly dip ladyfingers into the lemon syrup (1 second per side). Line the bottom of your dish.
• Spread half of your mascarpone cream over the ladyfingers, then spoon a layer of lemon curd directly on top of the cream.
• Add another layer of dipped ladyfingers, then the remaining mascarpone cream. Chill for at least 8 hours.
• Cover and refrigerate for at least 8 hours. This resting time allows the ladyfingers to soak up the moisture and become cake-like.
• Spread a final, smooth layer of lemon curd over the very top.