Peel the lemons almost superficially, leaving the white part of the citrus behind.
Half them and juice them (you should get about 4 cups of lemon juice). Save the seeds and place them in a small bowl with water.
Slice the peels transversally into very thin strips about 1/8 inch wide.
Wrap the seeds in a piece of gauze and tie it up (I used a square of surgical gauze). Reserve the water.
Place the lemon peel strips and lemon juice, the gauze with the seeds and the reserved water in a stockpot. Add 4 cups of water. Cook 1 hour at medium heat. Remove from the heat source and let rest for 24 hours.
The next day, remove the seeds and discard them. Place the stockpot back on the stove at medium-low heat, add the sugar and 2 cups of water and cook, stirring every 15 minutes, for about 1 1/2 hours, until the mixture thickens slightly to a consistency somewhere between syrup and jelly. Remove from the heat source and let rest for about 20 minutes (the mixture will thicken further).
While the marmalade is cooking, sterilize the jars: place them in a stockpot tall enough to cover them completely with water. Boil the jars for 10 minutes. Carefully remove them from the pot and let dry. Next, immerse the lids in the water and boil for 10 minutes. Remove carefully and let dry.
Fill the jars with the marmalade and close trightly. Place the jars in the stockpot where you sterilized the jars, cover them with water, bring to a boil, lower the heat to medium-low and process for 45 minutes. Remove the stockpot from the heat source. You can let the jars cool down in the water until it comes down to room temperature or carefully remove them from the hot water using an oven mitten.
When the jars are cool enough to hadle, label them and store them. The marmalade will last for many months.
Notes
Making marmalade is a two-day process, so plan accordingly
Lemon marmalade makes for a delicious gift. Your friends will appreciate it!