We have apple trees here in California, and for every one I pick, at least twenty rots in my house or the yard.
Anyway: you slice them to 1/4 to 1/8 inch in thickness.
Lay them flat on a cookie sheet ... or anything else oven safe.
Between 8 pm and midnight, put them in the oven on its lowest setting. In the morning, between 6 and 8 a.m., they will be done and delicious.
Mine turned out better than any I ahve ever bought in the store.
Oven temperatures: My oven starts at the setting "WARM" and then has increments from 200 degrees. So, I put my oven at "WARM." The perfect temperature would be 150 degrees at 1,000 feet above sea level or less. I think my "WARM" setting was 180 degrees Fareignheit.