Wash and scrub the lemon. Slice the lemon as thinly as possible - either using a sharp knife or a mandolin. Dig out and discard the seeds. Discard both ends of the lemon.
Prepare an ice water bath and set aside.
Bring a pot of water to rolling boil. Add in the lemon slices and cook for about 1 to 3 minutes, until the lemon slices have softened. Remove the lemon slices and immediately transfer them into the ice water bath. Once the lemon slices have cooled completely, drain. Reserve 1 cup of the hot lemon water.
In a large shallow pan (large enough to hold the lemon slices in 1 layer), combine the cup of sugar and the reserved hot lemon water. Bring the syrup to a simmer and add in the drained lemon slices. Simmer the lemon slices for 1 hour. Transfer the candied lemon slices to a lined baking sheet. Let stand until ready to serve.