Add 1 tbsp lemon juice to milk and set aside for 10 minutes.
To a bowl, add all purpose flour, corn starch, baking powder, baking soda, salt, ground cinnamon and nutmeg. Whisk to combine.
To another bowl, add eggs and beat well. Add oil, sugar and mix well. Add milk, vanilla extract and lemon zest. Whisk to combine.
Peel apples. Grate enough apple to get 3/4 cup. Slice remaining apples 1/4 inch thick to decorate top of cake.
Add dry ingredients (1st bowl ) to wet ingredients (2nd bowl). Whisk to combine. Add grated apple and mix. Pour into a buttered, parchment lined 8x2 inch cake pan.
Heat Air Fryer to 325 F/163 C and set time to 35 minutes. After air fryer is finished preheating, using oven mits, carefully place cake pan into hot basket. Cook for 30 minutes and check cake's doneness. Cake is done when toothpick inserted into middle comes out clean or with few crumbs. Cooking time can be up to 45 minutes depending on your air fryer. Mine took 40 minutes.
Cool pan completely on a wire rack. Run an offset spatula around sides of cake and turn over onto a plate or tray. Turn over onto your serving platter. Slice and serve as is or with powdered sugar on top.
***If you don't have cornstarch, it's fine to use only all purpose flour.