Prep the pan. Line your pan with parchment, leaving overhang for easy lifting. Lightly grease the sides. Make sure the pan fits in your air fryer basket with room for air to circulate.

Preheat the air fryer. Heat to 320°F (160°C) for the crust. Preheating helps the crust set quickly and bake evenly.

Mix the crust. In a bowl, whisk flour, powdered sugar, and salt. Stir in melted butter and vanilla until a soft, sandy dough forms. It should hold together when pressed.

Press and par-bake. Press the dough evenly into the lined pan, compacting it slightly up the edges for a clean border. Air fry at 320°F (160°C) for 10–12 minutes, until the edges are lightly golden. Keep the pan level as you remove it.

Make the filling. While the crust bakes, whisk eggs, sugar, and salt until smooth but not foamy. Whisk in flour (or cornstarch) until no lumps remain. Add lemon juice and zest. The mixture will be loose and glossy.

Lower the heat. Reduce the air fryer temperature to 300°F (150°C) to prevent over-browning.

Pour and bake. Pour the filling over the hot crust. Return the pan to the air fryer and bake at 300°F (150°C) for 12–16 minutes, until the center is just set and barely jiggles. The top should look matte, not wet.

Cool completely. Transfer the pan to a rack and let the bars cool to room temperature, about 1 hour. Then chill for at least 1–2 hours for clean slices.

Dust and slice. Lift out using the parchment. Dust with powdered sugar and cut into squares or bars with a sharp knife, wiping the blade between cuts.