Preheat the oven to 350F. Line two large baking sheets with parchment paper. Place a large round piping tip in a large piping bag.
Place the egg yolks, ¼ cup sugar, vanilla, and salt in a large mixing bowl. Beat on medium speed until pale and fluffy.
Place the egg whites in a separate bowl. Using clean beaters, beat on high speed until soft peaks form. While beating, add in the remaining ¼ cup sugar a spoonful at a time. Beat until the egg whites are thick and glossy, about 2 more minutes.
Beat the egg yolk mixture again just to remix, then fold the egg whites into the egg yolks in batches until well combined. Sift the flour and cornstarch into the egg mixture and fold until no dry streaks remain. (If the batter is a little lumpy, that’s okay. Don’t over-mix the batter.) Transfer the batter to the prepared piping bag.
Pipe the batter into 4-inch long logs (about 1-inch wide) on the baking sheet, spacing them about 2 inches apart. Dust one sheet generously with powdered sugar.
Bake the dusted sheet for 12 to 15 minutes or until lightly golden and firm to the touch. Let cool completely on the baking sheet. Dust the remaining baking sheet with powdered sugar and bake again as directed. Use or store immediately after they cool, as they will soften the longer they are exposed to air. Ladyfingers can be stored in an airtight container at room temperature for up to 2 weeks.
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Notes
Don’t skip dusting the dough with confectioners’ sugar before baking! The sugar helps the cookies bake up taller and airier rather than spreading and getting too thin.
A shorter bake time will result in a slightly softer and chewier cookie, and a longer bake time will yield a crisp, more golden cookie. Both are delicious, but you can decide how you’d like to enjoy them! If used in tiramisu, I lean towards a darker, crisper cookie for flavor and soaking up the coffee syrup.
Make sure to measure the flour correctly. The dough will dry if you add too much flour, and your ladyfingers won’t be light and airy. The ideal way to measure flour is with a kitchen scale. If you don’t have one, fluff your flour with a spoon, sprinkle it into your measuring cup, and use a knife to level it off.
It is essential to have a clean and dry bowl for whipping the egg whites. The egg whites also cannot contain any egg yolk. You will have difficulty whipping up the whites if the bowl is not completely clean or yolk-free. Avoid using a plastic bowl, as it’s more likely to hold onto grease.
Eggs are easier to separate when cold, but you get better volume with egg whites closer to room temperature. I recommend separating them in advance.
When folding in the egg whites, turn the mixture in on itself with a cutting motion, not a stirring motion. This way, you do not deflate the egg whites.
You can print a template and place it underneath the parchment paper if you want perfectly uniform ladyfingers. Just make sure you remove the template before baking the cookies.