Mix flour, cornstarch, baking powder, and salt in a bowl. Set aside.
In a large bowl, beat the butter and the other half (120 gr) of sugar until creamy and pale on medium-high speed. Scrape down the sides and up the bottom of the bowl with a rubber spatula as needed. Add vanilla and mix to combine.
Reduce speed to low and mix half of the flour mixture until just combined. Add milk in three additions, scraping down the mixing bowl with a spatula, and turn the batter over several times to ensure all of the ingredients are well incorporated. Add the remaining half of the flour; beat just until combined. Do not overmix the batter.
Using a large spoon or spatula, gently fold in the whipped aquafaba into the batter, taking care not to deflate all of the air you have incorporated.
Transfer the batter to a piping bag with a 1/2-inch round tip.
Pipe 3-inch lines of batter about 1 inch apart onto the parchment paper. Refrigerate the pipped ladyfingers for 20 – 30 minutes.
Preheat oven to 350°F (180°C). Line 2 cookie sheets with parchment paper, set aside.
After the chilling time is over, dust cookies generously with powdered sugar.
Bake the ladyfingers for 15 - 18 minutes, or until slightly golden on top and around the edges.
Allow to cool in the baking sheet for 5 minutes, then transfer to a wire rack to cool completely. Dust with more powdered sugar, if desired.