Wash, peel, and remove the core of the peaches (or use 24 ounces of frozen peaches). Slice them into ¼-inch thick slices. Add the sliced peaches, brown sugar, flour, lemon juice, cinnamon, nutmeg, vanilla, and salt to a large bowl. Use your hands to gently combine everything so the peaches are well-coated. Let the peaches sit at room temperature until they form a syrupy liquid in the bottom of the bowl, about 1 hour.