1. Scrub oranges. Cut in half lengthwise and slice as thinly as possible. Cut slices into eighths, reserving all juice. In a medium bowl, combine slices with water and zest, cover, and let stand at least 12 hours.

2. Transfer mixture to a large stainless-steel saucepan over medium heat and bring to a boil. Simmer 30 minutes; add lemon juice.

3. Measure total volume of fruit and liquid and add 3/4 cup sugar for every cup. Stir to dissolve and bring to a boil over high heat. Boil 30 to 60 minutes, until mixture reaches 221 degrees on a candy thermometer or falls in sheets from a spoon.

4. Pour into sterilized jars, seal, and cool.