Cored and sliced apples or other fruits.
Filtered water — use enough to reach about 1/3 the height of the height of the apples (so if the pot is filled halfway to the top with fruit, add water to fill the pot about 1/6 way to the top with water). The amount of water will vary with the water content of the fruit, but this is a good place to start.
pinch of salt

Add water to fruit pieces in a pot. Best would be a ceramic coated metal pot, or glasswear such as Pyrex or Corningware. With metal pots there is an interaction between food and metal surface, with non-stick coated cookware there is some migration of plastic into the food. Simmer until fruit is very soft. Put in food processor or blender, only adding enough of the fluid to achieve the consistency to the sauce that you prefer. Process until the sauce is your preferred consistency. Any extra beyond what you can eat in 3-4 days should be put in serving sized containers and frozen. Freezer bags work, although again I recommend glass containers to avoid migration of plasticizers. Fill glass containers ¾ full to allow for expansion as the sauce freezes.