Bring to boil in six cups of water, simmer 4 hours, add cooking water every hour to prevent burning, then cool in the cooking water.

Quarter whole fruit and chop to pulp in your food processor. Will make 2 cups. Put in dutch oven. Add equal amount of sugar. Put back in cooking water. Simmer without lid till water has evaporated and you have a thick dark brown carmelized marmelade.

Do the drip test: to make sure lemon is concentrated enough, drip a drop of mix along vertical plate. If it does not run, like on the left, marmelade is ready. If it runs, like on the right, simmer longer.

Sterilize lemon marmelade: ladle marmelade in mason jars, lid on, put in dutch oven, fill with water to rim of jars, bring to boil, tighten the lids, place upside down on kitchen towel, cool. Test for vacuum. If good vacuum, store in pantry. If not sure, store in fridge.