Wash lemons thoroughly, removing all dirt and leaves.
Zest lemons, removing all the colorful skin with a zester or vegetable peeler. Leave as much of the white pith as possible. Save the zest for another use.
Cut lemons in half and juice them with a hand juicer. Save the juice in a large bowl.
Remove any seeds you find and save them in a small bowl.
Separate the spent fruit from the rind and throw away the fruit.
Chop the remaining rind into 1/4-inch chunks.
Place rind, water and 1/2 cup of saved lemon juice into a large non-reactive pot.
Let rinds sit in the water for 1-2 hours to soften.
Bring pot to boil over high heat.
Reduce heat to medium-low and simmer for 10-15 minutes. Do not let the rinds boil dry. Keep an eye on the liquid level.
Strain the mixture over a cloth-lined colander into another large pot. Cover the mixture and allow to strain overnight at room temperature.
Remove the mushy peels and seeds from the colander and bring the strained liquid back to a boil over medium heat.
Simmer gently until liquid has reduced by almost half. Remove from heat and allow to cool to room temperature or can for later use.