Preheat your oven to 325º.
Wash and peel the peaches. I like to just use a veggie peeler to get the skin off, but you can also blanch them, then shock in ice water and peel by hand that way.
Dice the peaches into mostly uniform chunks. The easiest way to do this is to cut off a large slab from one side, getting as close to the pit as you can, then rotating and continuing this procedure on the other sides. Then cut those slabs into strips and from there to cubes. The size of your dice is flexible but the larger the dice, the bigger the chunks after they cook down. So take that into consideration when dicing. I recommend about ½ - ¾” cubes.
Place the diced peaches into a large oven-safe pan. I like to use my glass 9”x13”, but this works with sheet pans too as long as there is a good lip on the sides. Remember, these peaches will get juicer before they start to cook down, so make sure the juice is contained.
Add all the rest of the ingredients to the pan with the peaches. Scrape the seed from the vanilla pod and chuck the cleaned pod in there with the peaches. If using vanilla bean paste, wait to add it at the end of roasting.
Mix to combine, making sure to thoroughly coat the fruit and distribute the ingredients. This helps break down the cell structure of the peaches, as well as allowing the sugar to maximize its ability to pull the juices out of the fruit.
Roast for 3-4 hours, stirring every 30 minutes to keep pieces from sticking to the edge of the pan and to keep the heat distribution even. The exact time depends on how juicy your peaches are—you're aiming for soft, jammy fruit with glossy, syrupy juices and very little visible liquid.
Allow the peaches to cool in the pan for 30+ minutes, then transfer to a container and allow to cool to room temperature before refrigerating them in an airtight container.
As soon as the peaches are at room temperature, they are ready to add to recipes, or use them warm on top of ice cream for an extra special summer treat!