Make sure your bowls and beaters are scrupulously clean before you start. I like to wash mine in super hot soapy water then allow them to air dry. Before starting, I give them a tiny swipe with a piece of lemon or paper towel with a tiny bit of vinegar. This ensures there is no oily residue on the utensils that might stop the egg whites from whipping.
Whisk together your flour and baking powder in a large bowl and set aside. Get your sieve out ready to go.
Preheat your oven to 180C/356F and arrange your oven racks to bake two trays of savoiardi at a time. Line two large baking trays with baking paper. I like to spritz some water on the tray first so the paper doesn’t slide around when I pipe. Sprinkle the baking paper with a thin but thorough layer of icing sugar.
Separate the eggs into two clean dry bowls. Transfer each clean egg white (meaning no hint of egg yolk has tainted it) to your whipping bowl before cracking the next egg. This ensures that no fat from the egg yolks gets into your egg whites.
Place the egg whites in your stand beater bowl or a large mixing bowl. Using a hand beater or your stand mixer with the beater attachment, whip the egg whites for 2-3 minutes. Once they are fluffy, gradually add 160g sugar. Continue beating for 3-5 minutes or until stiff, shiny peaks form.
If you are using one beater, wipe down the beating attachment. It doesn't need to be scrupulously clean as the egg yolks are not sensitive to fat like egg whites. Add the egg yolks and remaining 60g of caster sugar to your intended whipping bowl. Beat the mixture on a medium high speed for 3 minutes or so until it is light and creamy and looks slightly thickened.
Add the egg yolk mixture, vanilla bean paste, pinch of salt and lemon zest to the large bowl. Sieve in the flour and gently continue to fold until the flour is just incorporated. Some really small bits of flour are fine, but gently separate any large chunks. You should notice the mixture become more sticky when the majority of the flour is incorporated.
Place your piping bag in a long, tall glass and add the mixture to the bag, leaving plenty of room so the bag doesn't overflow. Twist the top to seal. Pipe the mixture into roughly 10cm biscuits in one even layer. You'll have mixture leftover for the next batch. Leave room between your savoiardi for a bit of spread.
Sprinkle the savoiardi with a bit more icing sugar to finish.
Place two trays of savoiardi in the oven for 7 minutes. Rotate the trays after this time so that they have equal time in the top and bottom of the oven. Continue to bake for 5-7 minutes or until lightly golden and thoroughly cooked through.
Remove the baked savoiardi from the oven and slide the baking paper off the trays. Repeat the process with the remaining batter. Keep in mind that the batter deflates a little as it sits, so your second round of savoiardi might be a touch flatter and more prone to spreading. Leave extra room between them to account for this.
Allow the savoiardi to cool completely before using them or placing them in an airtight container. Moist savoiardi will easily become soggy and break up as you dip them in the coffee liquid for Tiramisu.