Remove zest from lemons with a vegetable peeler. Remove any white pith from zest and lemon with a sharp knife. Blanch zest only in boiling water 5 minutes. Cut peeled lemons into quarters and discard seeds. Pur`zest, lemons, sugar, and water in a blender until smooth. With motor running, add oil in a slow stream, blending until “jam” is thick, and season with salt. Transfer to a bowl and chill, covered, 8 hours to allow flavors to mellow.