Before you start the recipe:

1. Zest and juice the lemons. You need to have 1 1/2 cups of lemon juice for both the soak and the curd. If the fresh lemons don’t quite cut it, just substitute whatever is missing with bottled lemon juice. You should also have about 1/4 cup of zest, but if it’s not quite there, don’t worry about it. The zest isn’t as important as the juice!

To make the ladyfingers (day before assembly):

1. Preheat the oven to 350 degrees and line two baking sheets with parchment paper. Fit a large (16-18 inch) pastry bag with a large round tip (I use an Ateco #808) and set aside.
2. Sift the flour and cornstarch together into a small bowl and add the 1 TB of lemon zest. Stir the zest into the flour until it’s evenly mixed. Set aside.
3. Add the room temperature egg whites to a large, clean mixing bowl. Add the egg yolks to a smaller bowl and set aside.
4. Measure out half (1/4 cup) of the caster/superfine sugar and place it near the bowl of egg whites so that you can easily grab it.
5. Using a hand mixer with clean beaters, beat the egg whites on medium high speed until very soft peaks form. When you stop the mixer and pull the beaters up, the peaks should sink down a little and not hold up well. 
6. Reduce the mixer speed to medium low and gradually add the 1/4 cup of caster sugar in small additions. Mix each one in completely before adding another. I like to add a couple teaspoons at a time and mix them in for about 5 seconds before adding more.
7. After all the sugar has been added, increase the mixer back to medium high and beat the egg whites until they form stiff, glossy peaks. When you raise the beaters up, the peaks should not move much, if at all. Set the egg whites aside, and leave the beaters in the hand mixer without cleaning them.
8. Add the remaining 1/4 cup of caster sugar to the egg yolks, along with the lemon extract/paste and salt. Use the hand mixer to beat the yolk mixture on high speed until it becomes thicker and pale, about 2-3 minutes.
9. Drizzle the egg yolk mixture over the egg whites and add the flour mixture. Use a spatula to gently fold the batter together. It will start out dry and chunky, but be patient and don’t get rough! Keep the folding motion gentle and rotate the bowl with each fold. The batter will come together in a few minutes, and have a lot of air holes. It won’t look like a smooth cake batter, which is fine! If you have a few stray egg white streaks, that’s okay. 
10. Carefully transfer the batter to the prepared piping bag, and pipe the cookies into 3 inch long logs on the prepared baking sheets. You only need to leave about an inch between the cookies, since they rise rather than spread.
11. After you’ve piped out all the cookies, dust them generously with the 1/2 cup of powdered sugar right before going into the oven. This gives the ladyfingers a much better rise! Don’t add the powdered sugar until immediately before you bake them. 
12. Bake the cookies for 18 minutes, or until light golden brown on the top and sides. They may crackle a bit on the top, which is normal.
13. Allow them to cool on the baking sheet for about a half hour before transferring to a cooling rack. Leave them out on the cooling rack overnight to dry out before using in the tiramisu.

For the limoncello soak:

1. Combine the 1 cup lemon juice and 1/4 cup granulated sugar in a small bowl and stir in the 1/4 cup limoncello. Continue to stir until the sugar has dissolved, and transfer the mixture to a wider, shallow dish for dipping the ladyfingers. Set the finished soak aside until you’re ready to assemble the tiramisu.

For the lemon curd mascarpone filling:

1. Add the 3 egg yolks, 1/2 cup granulated sugar, 1 TB lemon zest and 1/2 cup lemon juice to a saucepan or saucier. Whisk until incorporated and smooth, and continue whisking constantly over medium heat until the lemon curd has thickened to the consistency of set instant pudding. This can take 10-15 minutes, depending on your stove and pan, so it’s an arm workout! Be sure not to stop whisking, or the eggs will scramble.
2. Once the curd has thickened, remove the saucepan from the heat and immediately strain the curd through a fine mesh sieve to remove the zest. Add the curd to a plate or wide, shallow dish. This helps it cool down faster. The curd needs to be at a cool room temperature before adding to the mascarpone.
3. Once the lemon curd is at a cool room temperature, remove the mascarpone from the fridge and allow it to sit at room temperature for 20 minutes. After 20 minutes, add the mascarpone to a large mixing bowl and use the hand mixer to beat on low speed for 30 seconds to loosen it up a little. Add the 3 TB limoncello and beat for another 30 seconds until smooth and creamy.
4. Add the cooled lemon curd to the mascarpone and beat on low speed for 30 seconds until combined and smooth. Take care not to overbeat, so that the mascarpone doesn’t break or curdle. Fold in the whipped topping/whipped cream until fully combined and smooth, and refrigerate until you’re ready to assemble the tiramisu.

To assemble the tiramisu:

1. Starting with half of the ladyfingers, dunk each one in the lemon/limoncello syrup for a few seconds on each side. Line the bottom of an 8 x 8 square pan with the soaked ladyfingers in an even layer. You should use 10-12 cookies.
2. Spread half of the mascarpone filling on top of the soaked cookies and smooth the surface. Repeat for the remaining ladyfingers and mascarpone filling, smoothing the top.
3. Cover the tiramisu and allow to chill overnight. This makes sure that the ladyfingers have plenty of time to soak up the lemon syrup and become cake like, as well as giving the cream filling time to set up the rest of the way.
4. Keep any leftover sealed in the fridge for up to 3 days.