Cut 1 lemon into small cubes with the peel on. First, slice it into thin rounds, then into strips, and finally into small cubes. Place them in a small saucepan.

Zest the yellow part of the remaining 3 lemons (avoid the bitter white pith). Add the zest to the same saucepan.

Peel those 3 zested lemons completely. Chop the flesh of them removing all membranes and seeds. Set the chopped lemon flesh aside for now.

Pour enough water into the saucepan to cover the lemon cubes and zest. Bring to a boil, then reduce the heat and simmer for 10 minutes.

Drain using a fine strainer and discard the water. Return the lemon cubes and zest to the saucepan.

Add the reserved chopped lemon flesh to the saucepan. Pour in 2 cups of sugar and 2 cups of water. Stir well and bring to a boil.

Stir in the lemon juice and simmer for another 5 minutes. Remove from heat and let it cool. The jam will continue to thicken as it cools.

Transfer to a clean jar and keep in the refrigerator for up to 2–3 months.

For longer storage, pour the hot jam into a sterilized jar, seal tightly, and turn it upside down. Let it cool completely at room temperature, then store in a cool, dry place or in the fridge.