Sloe jelly : sloes in pan. Add water. Lemon juice. Cook. Mash. Filter through a jelly bag /cloth overnight. Measure juice. Each ml of juice needs a gram of sugar. Boil up to setting point, pot.
Take the spent mush, add to the same (ish) volume of cooking apples, lob in some water. Cook, mash, another night in (a clean) jelly bag.
Same ratio sugar to juice, pot.