Prepare the Lemon Syrup: Combine freshly-squeezed lemon juice, water, and granulated sugar in a saucepan over medium heat. Stir until the sugar completely dissolves, then let it simmer gently for about 10 minutes until slightly thickened. Remove from heat and allow it to cool while you prepare other components.

Make the Lemon Curd: In a separate bowl, whisk together egg yolks, whole egg, granulated sugar, salt, and lemon juice until smooth. Transfer this mixture to a saucepan over low heat and cook gently, stirring constantly until it thickens enough to coat the back of a spoon—about 10 minutes should do it! Once thickened, remove from heat and whisk in butter and lemon zest until well combined.

Whip Cream & Combine with Mascarpone: In another bowl, whip heavy cream until soft peaks form then set aside. In another large bowl, combine mascarpone cheese and remaining granulated sugar until smooth; gently fold in whipped cream until fully blended for a light and airy texture.

Assemble Layers of Flavor: Dip each Savoiardi ladyfinger briefly into your prepared lemon syrup before laying them flat in a serving dish or trifle bowl as your first layer. Spread half of your prepared lemon curd over the ladyfingers followed by half of your whipped mascarpone mixture; repeat these layers again finishing with a smooth layer of mascarpone on top.

Chill Before Serving: Cover your assembled Lemon Tiramisu with plastic wrap or aluminum foil and refrigerate for at least four hours or overnight if possible—this allows all flavors to meld together beautifully!