Preheat your oven to 300°F (150°C) and line two baking sheets with parchment paper.
In a bowl, sift together the all-purpose flour, cornstarch, and baking powder.
In a stand mixer with a whisk attachment, whip the aquafaba on high speed until stiff peaks form. Gradually add the caster sugar and continue whisking until the mixture becomes glossy. Then, mix in the oil.
Remove the bowl from the mixer and gently fold in the flour mixture until just combined.
Transfer the batter to a piping bag and pipe it into long strips on the lined baking sheets. Dust with powdered sugar and bake for 18-20 minutes, or until lightly golden.
For the lemon curd, combine all the ingredients in a saucepan over medium heat. Stir constantly until the mixture thickens. Remove from heat, and let it chill and thicken, ideally overnight.
To make the lemon mascarpone, whip the dairy-free butter in a stand mixer until it becomes pale and fluffy. Gradually add the powdered sugar, then mix in the lemon juice and dairy-free yogurt.
Assemble the tiramisu once everything has cooled and set. Start by mixing the ingredients for the lemon soak. Dip the ladyfingers in the lemon soak, then layer them with the lemon curd and lemon mascarpone. Finish with a layer of whipped cream and a sprinkle of lemon zest.