• I highly recommend that you use a mandoline slicer to thinly slice the apples for consistency in thickness as this affects how crispy the apple chips will be
• You don't need to peel the apple. Just wash them clean, pat them dry. I cored the apples using the apple corer. Some people just slice the apples without removing the core and manually remove the seeds later after slicing
  
• Slice the apple thinly, about 1/8-inch in thickness using a mandoline slicer. Sprinkle with some ground cinnamon and lightly toss them, taking care not to break the apple slices into small pieces
  

If baking in the oven:

• Preheat the oven to 220 F (105 C) for conventional oven, 200 F (93 C) for convection oven. Position one oven rack on the upper 3rd and another one on the lower 3rd. Line two large baking pan with parchment paper or silicone mat (which is what I used)
• Arrange the apple slices very closely on the prepared baking pans, in one layer.
  
• Place the pans on the positioned racks and bake for 1 hour.
  
• After one hour, remove the pans from the oven and flip the slices and return back to the oven and make sure to rotate the pan, top to bottom, front to back for even baking
  
• Bake for another 1 1/2 hours in the oven. When the time is up, turn off the oven, but DO NOT open the oven door. Let the apple slices "cured" in the oven for another 2-3 hours or longer if possible. This makes them stay crispy longer.
• After that remove from the oven. They may still feel soft when they are warm, but they crisp up once they have cooled down. They should be crispy when they have cooled down

If using an air-fryer:

• Spray the basket of the air fryer with some cooking spray. Arrange the slices of apples in one layer and then arrange the second layers, overlapping is fine. I arrange about 3 layers. Try not to arrange too many layers at one go. That's why if you are using an air-fryer, you don't want to make a huge batch because you are limited by the space in your air fryer
  
• Air fry at 300 F (150 C) for 10 minutes and check. You will see the apple slices are all over the place because of the forceful hot air in the air fryer, that's normal,
  
• Just rearrange the slices again, give them a shake and then air fry for another 8-10 minutes. Let them cool down for about 15 minutes and see if they have crisped up. If not, you can air fry for another 3-5 minutes and check again. The cooking time depends on the moisture content of the apples. So, you will have to experiment with the time
  

If using a dehydrator:

• My oven and air fryer have a dehydrator function and that's what I use. The air fryer comes with a 3-tier tray to dehydrate food. Arrange the apple slices closely, in one layer on the tray.
  
• The dehydrator temperature is 180 F for my air fryer and I set the time to 10 hours. The dehydrator in the oven starts at 150 F and I set the time to 12 hours.
  
• The longer you dehydrate them, the crispier they are.
  

Storage:

• Regardless of which method you use, let the chips cool down completely before storing. Store them in an air-tight container to maintain crispiness. If it's humid where you are, you may notice that they may lose their crispiness much quicker
• Read my post details below to see which method is my favorite and which one stays crispy the longest