Begin by washing 4 to 6 fresh lemons under cool running water to remove any residue. Slice the lemons thinly, about 1/8 inch thick, and remove any visible seeds.

In a large saucepan, combine the sliced lemons with about 4 cups of water. Bring to a boil over medium-high heat, then reduce to a simmer and cook for 30 minutes.

Stir in 3 to 4 cups of granulated sugar over low heat until completely dissolved.

If using pectin, add it according to the package instructions. Increase heat slightly and let it simmer for another 10 to 15 minutes.

Remove from heat and let cool for about 5 minutes. Pour the hot jam into sterilized jars, leaving some space at the top.

Allow jars to cool to room temperature, then check seals by pressing the center of each lid.