• Heat the air fryer to 320°F (177°C). Place 2 sheets of graham crackers in a ziplock bag, seal, and roll with a rolling pin or heavy can to crush. This yields about ¼ cup of crushed graham crackers. Alternatively, you can add the cookies to a food processor and pulse until the cookies turn to crumbs.
• Pour the cookie crumbs into a small bowl and stir in the sugar and melted butter.
• Pour the crumbs into a 10-ounce ramekin. Using your fingers or the back of a spoon, press the crumbs gently so they form a crust on the bottom.
• Bake the crust for 5 to 6 minutes. Then, remove it from the oven and set it aside to cool.

Make the filling

• Increase the air fryer temperature to 350 degrees F. Whisk the egg yolk in a small bowl and set aside.
• In a 1-quart saucepan, mix sugar and cornstarch; gradually stir in water. Cook over medium heat, stirring constantly until the mixture thickens and begins to boil. Once thickened, reduce the heat to low.
• Stir 1 to 2 spoonfuls of the hot mixture into the egg yolk to temper the yolk. Then, in a slow and steady stream, whisk the egg yolk mixture into the saucepan. Bring the heat to medium and cook until the mixture is thick and begins to bubble, stirring constantly. Remove from the heat and stir in butter and lemon juice.
• Place the ramekin into the air fryer basket and cook for 5-8 minutes.

Make The Air Fryer Meringue:

• Beat the egg white and cream of tartar with an electric mixer on medium-high speed until foamy, about 2 minutes.
• Beat in sugar, ½ tablespoon at a time; continue beating until stiff and glossy.
• Spoon the meringue over the pie filling and spread evenly over the top. Carefully seal the meringue to the edge of the crust to prevent "shrinking".
• Bake until the meringue is golden brown, 3 to 6 minutes.
• Transfer to a wire rack and let cool completely to room temperature. If the pie is even slightly warm when you cut into it, the lemon filling will be runny.
• Cover and refrigerate the cooled pie until you are ready to enjoy it. Store in the refrigerator.