In a medium-sized mixing bowl, stir together the flour, 1 cup of powdered sugar, baking powder, baking soda, and salt. 📷
Using a stand mixer, beat the aquafaba on medium speed until it becomes foamy, which should take about one minute. Add the cream of tartar and beat on high speed for 3 minutes. Scrape down the sides of the bowl and add the caster sugar to the aquafaba 1 tablespoon at time, beating for 30 seconds in between each addition.
Gently fold the dry ingredients into the aquafaba until they're just barely combined. Don't over mix.
Transfer the mixture to a piping bag with a ½-inch diameter piping tip or a ziplock bag with a corner snipped off. Pipe the batter into 3-inch strips, leaving about 1-inch between each ladyfinger, since they will flatten out and spread as they bake.
Dust the ladyfingers with powdered sugar. Bake at 375˚F / 175˚C for 12-14 minutes, until edges are golden brown. Let cool for 10-15 minutes, then transfer to a cooling rack to cool completely before using.