Mix Dry Ingredients: Mix together the cornstarch, all-purpose flour, salt, baking soda and baking powder in a bowl and set aside.
Cream Butter and Sugar: In another bowl, cream together the plant-based butter and sugar using a handheld electric mixer until combined, about 1 minute. You can also use a stand mixer where the handheld mixer is noted.
Add Aquafaba and Vanilla: Add the aquafaba and vanilla extract to the butter-sugar mixture and cream for about 3 minutes, until light and fluffy. Don't worry if it doesn't come together into a smooth mixture, it will when you mix in the flour.
Combine Batter: Add half of the flour mixture into the creamed butter and sugar mixture and mix until just combined. Add the almond milk and the remaining flour mixture and beat until combined and smooth, about 30 seconds to 1 minute.
Pipe Ladyfingers: Add the batter into a piping bag with a round tip or into a zip top bag with the corner cut off. Pipe the ladyfingers onto the baking sheets, leaving about 1-inch of space between each. You should get 25-30 ladyfingers. If you do not have a piping bag or ziplock back to pipe the ladyfingers, you can shape them with your hands. Each cookie should be roughly 1-inch wide and 2-2.5-inches long.
Chill: Place the ladyfingers in the fridge to chill for 30 minutes.
Preheat Oven: After 20-25 minutes of chilling time, start preheating the oven to 350℉.
Bake: Bake the ladyfinger for 15 minutes, until the edges are golden and lightly crispy. Set aside to cool completely on the pan.