Start by coring and chopping the quince, and then place it in a stock pot with 3 quarts of water.

Bring the mixture to a boil, and then turn it down to a low simmer. Cook for 2 to 3 hours, until the liquid has reduced by about half and the quince are a rose-y pink color. (Don't let the liquid reduce by more than half, and if it's cooking too fast, add more water.)

Turn off the stove and strain the mixture thourhg a jelly bag or a fine mesh strainer lined with a double layer of dampened cheesecloth. Allow the mixture to drain for 2 to 3 hours, until you have about 5 cups of liquid collected. (Do not squeeze to extract more juice, just let it drain naturally. Squeezing will result in a cloudy jelly.)

If canning, prepare a water bath canner, jars, lids and rings at this point.

Measure the extracted juice, you should have about 5 cups. (If you have slightly more or less, no worries.)

Place the measured quince juice into a clean jam pot. Add 1 cup of sugar for each cup of quince juice, adjusting the amount to the amount of juice you extracted.

Add in about 1/2 cup of lemon juice, or the juice of 2 to 3 lemons. Stir to incorporate.

Turn on the stove to high heat and bring the mixture to a boil.

Cook over high heat until the jelly sets, about 15 to 25 minutes. Quince jelly sets at 220 degrees F (105 C) at sea level. That drops by 1 degree for every 500 feet in elevation above sea level, and a 1,000 feet it'll set at about 218 F. Alternately, test for set on a plate that's been chilled in the freezer.

Once the quince jelly is done, remove it from the heat and ladle into prepared jars, leaving 1/4 inch headspace.

If canning, process jars in a water bath canner for 10 minutes (or 15 minutes if above 6,000 feet in elevation).

Once the processing time is complete, use a jar lifter to remove the jars to cool them completely on a towel on the counter.  Check seals after 12 to 24 hours, and store any unsealed jars in the refrigerator for immediate use.