1. Rinse the citron fruits well and grate them using the fine side of the grater. Score them with a knife in 3 places. Set them aside for a little while, then remove the peel. Next, remove the inner pith/fibers. Roll them into a cylinder shape and secure them with toothpicks. Make sure the cut edges meet and face downwards so they don't break apart or slip off the toothpick. Place them in a pot and put a plate on top. Pour plenty of water to cover them. Let them boil vigorously for about 10 minutes, until they soften.
2. Remove the hot water and add cold water. Once the water boils, turn off the heat. For 5 days, change the water, adding lukewarm water each day, without putting it on the heat. On the 6th day, boil them well until they vigorously bubble, strain them, remove the toothpicks, place them back in the pot, and add the sugar while they are still hot. Let them sit for 5-6 minutes so they release their water, then add enough water to cover them.
3. Boil for 10 minutes and turn off the heat. The next day, boil until the syrup thickens. At the end, add the lemon juice. Leave the spoon sweet in the pot to cool completely. Put the sweet preserve into sterilized jars and turn them upside down.
