Wash the peaches thoroughly, then remove the core and cut out the bad parts.
Preheat the oven to 180 degrees on the bottom-up baking programme.
Cover a high-sided pan with vinegar so the jam won't burn. The vinegar will not be noticeable on the jam if you spread it thinly.
Fill the high-sided baking dish about halfway with the chopped peaches.
Once the oven is heated up, put the peaches in the oven and bake at 180 degrees for an hour on the top and bottom baking programme, then stir the peaches, they will start to release their juice. We put it back in the oven for another hour.
After 2 hours of baking, remove from the oven, season and sweeten to taste. If you want, you can add a preservative if you want to keep it for longer. Then turn the oven down to 100 degrees and return the jam to the oven for another 30 minutes. I make it a habit to put the jars in the oven with the jam to sterilise, including the clean jars and tops of course.
When the total baking time of 2.5 hours has elapsed, pour the hot jam into the hot jars. I also use tin foil just to be on the safe side, then pull the jars tightly over the top and turn them upside down for 10 minutes, then place them in a dry dutch oven and let them cool slowly.