Preheat the oven to 160 °C (fan/convection) and line two baking trays with greaseproof paper.
In a medium bowl, sieve together the plain white flour, cornstarch, fine sea salt and baking powder. Set aside.
260 g plain white flour, 2 tablespoon cornstarch, pinch fine sea salt, 1 teaspoon baking powder
In a spotlessly clean bowl of a stand mixer fitted with the whisk attachment, place the aquafaba and whip on high speed until stiff peaks form. Stop the mixer, add the caster sugar and whisk again until the mixture is glossy and falls in ribbons.
120 ml aquafaba, 140 g caster sugar
With the mixer still running, drizzle in the vanilla extract and the vegetable oil. Remove the bowl from the stand mixer and fold in the flour mixture until just combined and no lumps remain. Set aside on the counter to rest for 10 minutes.
2 teaspoon vanilla extract, 45 ml vegetable oil
Transfer the batter to a piping bag fitted with a round nozzle and pipe the mixture into half inch circles onto the lined baking trays, leaving space between each one for expansion. Wet a finger and dab on the top of each circle of batter to flatten into a neat dome.
Place in the oven to bake for 20-25 minutes or until golden brown. Remove from the oven, leave to cool for 5 minutes then transfer to a wire cooling rack to cool and crisp up fully.