Quince Preserves (Membrillo)

Wipe the fuzz off the quinces and rinse well. Peel each quince, cut in half, and remove the core and seeds. Reserve the peels, cores and seeds and place in a square of cheesecloth. Bring the corners together and tie securely with kitchen string.

Slice the quinces and place in a heavy pot, preferably one of enamel-lined cast iron. Add water to cover and the cheesecloth pouch. Place over high heat and bring to a boil. Reduce the heat to low and cook slowly, uncovered, until very tender, 20 to 40 minutes; the timing will vary from batch to batch. You may want to stop the cooking a few times, for about an hour or two, to let the quinces rest and redden. Add more water if the mixture begins to dry out. (This process can even be done over 1 or 2 days without refrigerating between simmerings.)

When the quinces are red and very tender, remove the cheesecloth bag and discard. Using a potato masher, mash the quinces, or puree them in a food processor. In the same pot, combine the pulp and cooking water, 3 1/2 cups of the sugar and the cinnamon. Place over low heat and cook very slowly, stirring often, until thick, about 20 minutes. Taste and add more sugar if the preserves seem too tart.

Ladle into hot, sterilized canning jars to within 1/4 inch of the top. Using a hot, damp towel, wipe the rims clean. Seal tightly with lids and screw bands. Process the jars in a hot-water bath for 10 minutes. Using tongs, transfer to a wire cooling rack, let cool to room temperature and check for a good seal. Label and store in a cool, dry place for up to 1 year. If the seal is not good, store in the refrigerator for up to 1 month.