Prepare the lemon curd: In a medium saucepan, whisk together the eggs, granulated sugar, lemon juice, and salt. Cook over medium-low heat, whisking constantly, until the mixture thickens and coats the back of a spoon—this should take about 8 to 10 minutes. Remove from heat, transfer to a bowl, press plastic wrap directly on the surface to prevent a skin, and let it chill for approximately 2 hours.

2. Make the lemon syrup: In a separate saucepan, stir together the sugar, lemon juice, and water. Heat over medium, stirring occasionally, until the sugar fully dissolves, about 3 to 4 minutes. Let the syrup cool completely.

3. Prepare the cream filling: In a stand mixer fitted with the whisk attachment, beat the mascarpone cheese and salt just until smooth, about 15 to 30 seconds. With the mixer running on medium speed, slowly pour in the cold heavy cream and vanilla extract. Continue beating until soft peaks form, about 3 to 4 minutes.

4. Assemble the tiramisu: Dip each ladyfinger quickly into the cooled lemon syrup and arrange them in a 9×13-inch baking dish to create a single layer. Spread half the mascarpone mixture evenly over the ladyfingers. Repeat with another layer of soaked ladyfingers and drizzle any remaining syrup on top. Finish with the rest of the mascarpone mixture, smoothing it into an even layer.

5. Chill & serve: Cover the dish tightly and refrigerate overnight. When ready to serve, spread the remaining lemon curd on top. Optionally, dust with powdered sugar.